To make the pastry, put the flour in a bowl, add the butter, and rub together with your fingertips until the mixture resembles breadcrumbs. Using a round-bladed knife in a cutting motion, combine the egg yolks with the mix until a pastry ball forms. Turn out on a lightly floured surface and quickly knead until the pastry is even and smooth, then wrap and place in the fridge to chill for 30 minutes.
Roll out the pastry on a lightly floured surface and line a 30cm push-up-bottom flan tin, making sure there are no cracks. Return to the fridge to
While the pastry is baking, make the filling. Melt the butter with the oil in a saucepan. Add the finely sliced onions and
Mix the cream, eggs, nutmeg and seasoning in a bowl. Put the cooked onions in the baked pastry case, carefully pour in the egg mixture and then return the tart to the oven to