Preheat the oven to 200C/180C Fan/Gas 6. Line a baking tray with baking paper. Put the butter in a pan with 150ml cold water and a pinch of salt. Heat until the butter melts and then bring it to the boil. Once boiling, remove immediately from the heat and add all the flour at once. Beat hard with a wooden spoon until it forms a dough that leaves the sides of the pan clean. Tip into a large bowl and leave to cool for 15 minutes.
Gradually beat the eggs into the dough - you can do this with a wooden spoon or electric hand mixer. Put the mixture into a freezer bag and snip off one corner. Use this to pipe a 20cm ring on the baking tray.
Sprinkle the almonds on top. Bake for 30 minutes, without opening the oven, or until puffed up and golden. With a knife, make small holes round the edge (to let steam escape). Return to the oven for 5 minutes, then cool on a wire rack.
Mix the mascarpone with the icing sugar, vanilla and milk. Slice the ring in two and fill with the mascarpone and fruit. Dust with icing sugar.