Put the butter and sugar in a bowl and beat with an electric whisk until pale and creamy. Fold in the flour and cocoa with a pinch of salt until it forms a dough. Press evenly into the base of a 20x30cm brownie tin using a spatula. Prick all over with a fork and chill for at least 30 mins.

Heat the oven to 180C/160C fan/gas 4. Bake the base for 15-20 minutes until it looks dry and firm. Meanwhile, for the filling, melt the butter and chocolate in a heatproof bowl over a pan of simmering water until smooth. You can also do this in the microwave, stirring between short bursts. Leave to cool slightly while you whisk the eggs, egg yolk and sugar in a bowl with an electric whisk until pale and fluffy.

Lower the oven to 160C/140C fan/gas 3. Fold the slightly cooled buttery chocolate into the eggs, then fold in the cocoa until completely combined. Pour into the tart case and top with mini chocolate eggs.

Bake for 15 mins until the filling has set and the pastry case shrinks away from the sides of the tin. Leave to cool completely in the tin before loosening around the sides with a knife, and cutting into 20 slices to serve.