Gooey Butter Oat Pie

Bake the oat cookie. Heat the oven to 175 °C (155 °C fan). Beat the soft butter with both sugars until fluffy, then beat in the yolk. Mix in the oats, flour, baking powder, bicarbonate and salt until it forms a stiff dough. Press it about 6 mm thick into the lined tin and bake 15 minutes, until golden at the edges. Cool completely; the cookie needs to be cold to crumble well.

Press the crusts. Crumble the cookie into a bowl and rub in the extra brown sugar and salt. Stir in the melted butter until the crumbs clump when squeezed, adding a little more butter if they stay dry. Divide between the two tins and press firmly over the bases and up the sides.

Make the filling. Grind the freeze-dried sweetcorn to a fine powder. In the mixer on low speed, combine the sugar, brown sugar, milk powder, corn powder and salt. Add the melted butter and mix 2-3 minutes, then the cream and vanilla. Finally add the yolks and mix on low just until glossy and even; whipping in air would make the filling puff and crack.

Bake. Set the tins on a baking tray and divide the filling between them. Bake at 175 °C (155 °C fan) for 15 minutes, then turn the oven down to 160 °C (140 °C fan) and bake about 5 minutes more. The pies are ready when the edges are set and lightly browned but the middle still wobbles like thick custard.

Freeze. Cool on a rack, then freeze the pies for at least 3 hours. Chilling hard sets the buttery centre into its dense, fudgy texture.

Serve. Serve cold, dusted with icing sugar, cut in thin wedges.