Preheat the oven to 400°F (200°C).

Butter six ramekins or custard cups.

Dust each with cocoa powder and tap out any excess.

Put a heaping tablespoon of dulce de leche in each cup.

Divide the flaky salt among them by sprinkling it over the dulce de leche.

Put the custard cups on a baking sheet.

In a bowl set over a pan of simmering water, melt the chocolate with the butter, stirring until smooth.

Remove from the heat and stir in the cocoa powder and the brown sugar.

Mix in the eggs, one at a time.

Divide the chocolate mixture among the custard cups.

Bake for 15 minutes, or until the sides are firm but the center is still shiny and quite jiggly.

Let the cakes cool for at least 5 minutes before serving.