Step 2

Beat the softened butter and sugar together in a stand mixer until creamy.

Step 3

Add the flour and salt and knead by hand until a smooth dough forms. Divide into two equal pieces.

Step 4

Line the base of a square or round cake pan (not a springform pan) with parchment paper. Press the first half of the dough into the pan, flattening with fingers and a spoon.

Step 5

Spoon dollops of dulce de leche evenly over the base. Sprinkle over the chopped dark chocolate.

Step 6

Place the second half of dough on top and press to cover. Brush with the beaten egg.

Step 7

Bake for about 30 minutes until golden-brown. The cake will feel wobbly — this is normal; it firms up as it cools.

Step 8

Leave to cool completely, about 1 hour, before cutting into small pieces.