Roll out the pastry on a lightly floured surface and cut into 12 pieces, roughly 8cm square. Use each piece to line the holes of a 12-hole muffin tin and use a ball of trimmings to press the pastry right down into the corners.
Press a large piece of foil over the tin and down into the holes, then fill each with baking beans.
Bake for 15 mins until puffed up and golden, then remove the foil and cook for 10 mins more. Dont worry if the pastry puffs right up.
Meanwhile, trim the asparagus and separate the stalks from the tips. Bring a large pan of water to the boil, cook the stalks for 6 mins, then fish them out and place in a bowl of iced water. When cold, drain them again. Cook the tips separately for 3 mins, then place in the iced water.
Put the stalks, mascarpone and eggs into a small bowl, season generously with salt and pepper, then use a hand blender to blitz everything to a frothy green custard.
Use a spoon to push the pastry back down into the holes and fill each with the custard. Drop an asparagus tip into each, then crumble over the goats cheese. Return the tarts to the oven for 10-15 mins until the custard has puffed up and set. Leave to cool before removing from the tins.
