Whisk the egg whites in a large, clean bowl until soft peaks form. Whisk in the icing sugar in 3 or 4 batches, whisking well between each addition. Add a couple of drops of colouring with the final addition of sugar. Keep whisking until the mixture is light pink, with no streaks, and is thick and glossy, a bit like shaving foam.
Using a large metal spoon, gently fold through the ground almonds. Cover 4 baking sheets with baking parchment and dab a little of the mixture in the corners of each sheet to secure paper. If you don’t have enough baking sheets, make and cook half the quantity, then repeat. Use 2 spoons or a piping bag fitted with a wide nozzle to make 40 circles, each about 5cm wide. Leave to sit out for about 10 mins until a skin starts to form.
Heat oven to 180C/160C fan/gas 4. Place the baking sheets in the oven, leaving the oven door slightly ajar to allow steam to escape, then bake for 20-25 mins until just crisp, but not browned. Leave to cool.
When ready to serve, gently ease off the paper with a palette knife. Carefully spread 1 tsp raspberry jam per biscuit over half of the biscuits and 1 tsp mascarpone per biscuit over the other halves, then gently sandwich together.