Beat the eggs and sugar using an electric whisk until pale and doubled in volume. Slowly pour in the chocolate mix, folding it in, then fold in the flour, cocoa powder, the 1 tsp espresso and a pinch of salt. Pour into the tin, smooth out, and use the back of a spoon to make nine equally spaced dips in the surface. Divide the condensed milk mixture between them, then use a skewer to swirl it, creating a marbled effect. Bake on the middle shelf of the oven for 20-25 mins until cracked and shiny with a slight wobble in the middle. Leave to cool completely in the tin, then cut into squares. Will keep in an airtight container for five days, or in the freezer for three months.
Healthy chocolate brownies
Heat the oven to 190C/170C fan/gas 5 and line a shallow 23cm square baking tin with baking parchment. Tip the beans, cocoa, coffee granules, xylitol, vanilla, eggs and yogurt into a large bowl. Blitz using a hand blender until smooth. Or, do this in a food processor. Add the baking powder, then blitz again.
