Butter Pie

Method

1. Make the pastry first. Put 70 g of plain flour and 1 pinch of fine salt in a bowl, add 32 g of chilled diced butter and rub it in with cold fingertips until the mixture looks like coarse breadcrumbs with a few flakes still visible. Sprinkle over 2 tsp of cold water and bring it together into a firm dough with a knife, handling it as little as possible. Flatten into a disc, wrap and chill for 20 minutes.
2. Peel 200 g of floury potatoes and slice them into rounds about 3 mm thick. Drop them into a small pan of well-salted boiling water and par-boil for 5 minutes, until the edges are just yielding but the slices still hold their shape. Drain in a colander and spread out to steam dry and cool completely, or they will steam the pastry.
3. Slice 70 g of onion as thinly as you can, into half-moons. Heat the oven to 200C (180C fan) and put a baking tray on the middle shelf to heat, which helps crisp the base.
4. Cut off one third of the chilled pastry for the lid. Roll the larger piece on a lightly floured surface to about 3 mm and line a 12 cm pie tin or small enamel dish, letting the edges overhang. Roll the reserved third into a lid a little larger than the tin.