Melt the butter, without letting it boil. Once melted set it aside while making the batter.
55 g butter
In a bowl add the egg and granulated sugar. With a hand whisk, mix well together until smooth and combined. About 1 min. Add the vanilla extract and gently mix it in.
1 large eggs, 50 g granulated sugar, ¼ teaspoon vanilla extract
In a separate small bowl mix together the flour, unsweetened cocoa powder, baking powder and salt. Then sift it over the bowl with the wet ingredients and gently mix it together until just combined.
45 g all-purpose flour, 10 g unsweetened cocoa powder, ⅛ teaspoon baking powder, 1 pinch salt
Now carefully add the melted butter and with a spatular fold it into the batter until combined. Cover the batter so the cling film touches the surface of the batter and refrigerate the batter at least 2 hours.
Once there is about 30 min until the batter is done in the fridge, preheat oven to 190ºC and place the Madeleine mold in the freezer.
If using a metal pan brush the Madeleines pan with melted butter, if using a silicone mold like I do, then this skip this step.
Add the Madeleines batter to a piping bag or use a spoon to fill the Madeleines silicone mold with batter. Fill the each cavity ½. Then with a small spoon spread out the batter so cover the base of the mold. The add a dollop of the dulce de leche in the middle of the madeleine. Pipe the remaining batter on top, making sure to cover all of the dulce de leche so nothing leaks out. It should reach to 9 Madeleines.
A can of dulce de leche
Bake for 10-11 minutes or until the signature bump has appeared. Allow the Madeleines to cool for 2 min. Then gently lift them out of the Madeleine silicone mold and let them cool down on a cooling rack while making the chocolate cover.