Step 1

Make the topping first. Using a sharp knife, slice off the skin and all pith from mandarins. Slip out the segments by slicing either side of the membrane. Remove any pips. Put mandarin segments in a bowl with the Cointreau and leave to soak. Squeeze juices from mandarin membranes and reserve. Cream butter and brown sugar in a small bowl, beating with a wooden spoon. Butter the sides of a 23cm cake tin, then spread the creamed butter and brown sugar over the bottom of the tin.

Step 2

Preheat oven to 180°C. To make the cake, put butter in a bowl and beat with an electric beater until creamy and loose, then beat in caster sugar and continue beating until fluffy and lighter in colour. Lightly beat eggs together in a small bowl. Gradually beat eggs into creamed butter and sugar, then sift over flour and fold in with a large spoon.

Step 3

Finely grate the zest from the orange. Strain mandarin segments and measure juices. Make up to ½ cup with any reserved mandarin juices, and, if necessary, freshly squeezed orange juice. Mix juices and orange zest into cake batter.

Step 4

Pat mandarin segments dry with paper towels. Arrange segments in tin on top of brown sugar and butter, starting from the centre. Spoon in cake batter and level top.

Step 5

Bake for 40 minutes, or until golden and springy to touch. Cool for 10 minutes in the tin, then cover with a large plate and invert. Leave for 2-3 minutes for butter and sugar glaze to trickle down over cake then lift off tin. Cool thoroughly before serving.