Dulce de Batata — sliceable sweet potato paste from the River Plate

i. Origin & history

Dulce de batata belongs to the Iberian tradition of fruit pastes — the most famous being Spanish dulce de membrillo, quince paste — brought to South America by Spanish and Portuguese settlers. In the Americas, cooks applied the same technique to local produce, and the sweet potato (batata, native to the tropical Americas) proved ideal: cheap, starchy, naturally sweet and able to set firmly when cooked down with sugar.

In Argentina and Uruguay, dulce de batata became one of the country's two great sliceable pastes, alongside membrillo. Both are sold in large tins and blocks in every supermarket, and they are pantry staples in a way few desserts are. The paste is made commercially on a large scale; the classic Argentine version is pale orange-brown, glossy and firm, and the chocolate version, dulce de batata con chocolate, has a ribbon of chocolate-flavoured paste through its centre.

Its most famous use is with cheese. A slice of dulce de batata or membrillo with a slice of mild, soft cheese — queso fresco, queso de máquina or port salut — makes the dessert called postre vigilante in Argentina, said to be named after the police officers ('vigilantes') who ordered it as a cheap, quick dessert in the cafés of Buenos Aires. It is also called queso y dulce, and in Uruguay and parts of Argentina, Martín Fierro, after the gaucho hero of José Hernández's epic poem.

Dulce de batata is also the traditional filling of many home bakes: pastafrola (a lattice-topped tart) and pepas (thumbprint biscuits). It is not to be confused with Brazilian doce de batata-doce, which is usually softer and spoonable, or with Japanese and Korean sweet-potato sweets.

ii. How sweet potato sets into a sliceable block

A firm dulce de batata depends on evaporation and starch. Cooked sweet potato is mostly water and starch; when it is puréed and cooked with sugar, water evaporates, the sugar concentration rises and the starch gelatinises and thickens. As the mixture cools, the starch sets into a firm gel, held together and preserved by the sugar. This is the same principle as membrillo, though quince relies on pectin rather than starch.

The ratio of sugar to sweet potato matters. Traditional recipes use roughly 700–800 g sugar per kilo of cooked sweet potato. Less sugar gives a softer, less stable paste that does not keep as long; more makes it very sweet and prone to crystallising. The sugar also acts as a preservative, which is why dulce de batata keeps for weeks.

Cooking time is the key judgement. The paste is ready when it is thick, glossy and pulls away from the base and sides of the pan in a single mass, and a spoonful dropped onto a cold plate holds its shape and sets firm within a minute. Undercooked paste stays soft and spreadable; overcooked paste darkens and can scorch. Commercial producers add a little gelling agent such as agar or pectin to guarantee a clean slice; home cooks sometimes do the same.

The cooking is messy: thick, hot paste spits and bubbles as it reduces. A deep heavy pan, a long-handled wooden spoon and a low-to-medium heat make it manageable.

iii. Ingredients

Makes 16 servings · scroll the side panel to adjust

• 1200 g sweet potatoes (to give about 1 kg peeled flesh)
• 750 g sugar
• 150 ml water
• 1 tbsp lemon juice
• 1 vanilla pod, split, or 2 tsp vanilla extract
• ¼ tsp salt
• 4 g agar-agar powder, optional, for a very firm slice
• 2 tbsp cocoa powder, for the chocolate version (optional)
• 60 g dark chocolate, chopped, for the chocolate version (optional)

In Argentina, batata is often a yellow- or cream-fleshed sweet potato that gives a pale, golden paste; orange sweet potatoes give a brighter colour and a slightly softer set, and both are fine. Weigh the peeled, cooked flesh and adjust the sugar to about three-quarters of its weight. Vanilla is the traditional flavouring; a strip of lemon zest is also common. Agar-agar is optional but gives the clean, firm slice of shop-bought dulce; without it, cook a little longer. For the chocolate version, a portion of the paste is mixed with cocoa and chocolate and layered through the middle.

iv. Method

1. Peel the sweet potatoes and cut into 3 cm chunks. Cover with cold water, bring to the boil and simmer for 15–20 minutes until completely tender. Drain well and purée until very smooth with a blender or food mill; you need about 1 kg of purée.
2. Put the purée, sugar, water, lemon juice, vanilla pod and salt in a deep, heavy pan. If using agar, whisk it into the water first.
3. Cook over a medium-low heat, stirring constantly with a long wooden spoon, for 35–50 minutes. The paste will bubble and spit; reduce the heat if needed and stir from the bottom.
4. It is ready when it is thick, glossy and darker, comes away from the pan in a single mass, and a spoonful on a cold plate sets firm within a minute. Remove the vanilla pod.
5. For the chocolate version, transfer a third of the paste to a bowl and stir in the cocoa and chopped chocolate until smooth.
6. Line a 20 × 10 cm loaf tin with baking paper. Pour in half the plain paste and smooth. If making the chocolate version, spread the chocolate paste over it, then top with the remaining plain paste.
7. Tap the tin to settle, cover with baking paper and cool at room temperature, then refrigerate for at least 6 hours, ideally overnight, until firm. Turn out and slice.

v. Tips & common mistakes

• Purée until perfectly smooth. Any fibres or lumps show in the finished paste. A food mill or blender gives the classic glossy texture.
• Drain the sweet potato thoroughly. Extra water from the boiling pan lengthens the cooking time considerably.
• Protect yourself while cooking. The thick paste spits violently. Use a deep pan, a long spoon and an oven glove on your stirring hand.
• Do not stop stirring. The sugar-laden purée catches quickly on the base; scorched paste tastes bitter.
• Use the cold-plate test. If a spoonful does not set firmly on a cold plate, keep cooking. Undercooked paste will never slice cleanly.
• Let it set fully. Slicing too soon gives soft, sticky pieces. Overnight in the fridge gives the cleanest cut.

vi. Variations

Dulce de batata con chocolate has a chocolate layer through the middle. Dulce de membrillo is the quince version, made in the same way. Dulce de zapallo uses squash or pumpkin, sometimes candied in pieces rather than puréed. Some home cooks add orange zest or cinnamon. As a filling, dulce de batata is softened with a little hot water and used in pastafrola, pepas and pastelitos.

For other sweets of the River Plate, see Argentina's dulce de leche, the biscuit cake chocotorta and Uruguay's meringue-and-peach chajá. Comparable fruit and vegetable sweets elsewhere include Indian petha and Indonesian dodol.

vii. Serving & storage

Serve slices of dulce de batata with an equal slice of mild, soft cheese as a postre vigilante — the classic Argentine café dessert — or on buttered toast for breakfast. It is also eaten on its own as a sweet, or used as a filling in tarts and biscuits.

Wrapped well in the fridge, it keeps for 3–4 weeks. Once cut, cover the exposed face with cling film to stop it drying and crystallising. It can be frozen for up to 3 months, though the texture becomes slightly softer after thawing.

ix. More from Latin American

• Dulce de Leche — Argentine milk caramel
• Chocotorta — Argentine biscuit icebox cake
• Chajá — Uruguayan meringue cake
• Manjar Blanco — South American milk caramel
• Cocadas — chewy coconut sweets
• Petha — Indian ash gourd candy