Heat the oven to 180C/fan 160C/gas 4. Spread the dulche de leche into the base of a 23cm square tin lined with baking paper. Beat the butter and sugar together until soft, sift the flour and baking powder together and stir in the almonds. Beat the flour mixture into the sugar and butter in 3 batches, adding an egg each time. Beat the mixture until smooth and then spoon it into the tin and level the top. Bake for 30 minutes or until a skewer comes out cleanly. Cool for 5 minutes and then invert the cake onto a rack and peel off the paper, don’t worry if a little caramel sticks to the paper, scrape it off and add to the top of the cake.