Citrus cake (citrus entremets)

Boil the mandarins 2 minutes, cover and leave overnight.

Next day, cut a mandarin into pieces, removing white membranes and seeds.

Pulse the candied orange peels with the sugar to grind; transfer to a pan with the grapefruit juice and cook down about 20 minutes until the moisture evaporates and it thickens.

Cool the marmalade to room temperature; it keeps chilled up to 2 weeks.

For pistachio paste, process pistachios with a bit of oil and almond extract.

Combine the lemon, mandarin and orange zest with eggs, sugar, pistachio paste and almond paste.

Warm the mixture to 122F (50C), then beat on high speed until cool, about 10 minutes.

Mix one third of the egg mixture with the melted butter, add the rest, and fold in the sifted flour.

Spread a quarter inch thick on a large baking tray lined with a silicone mat, covering twice the area of the 9-inch square pan.

Bake at 400F (200C) about 8 minutes.

In a saucepan combine lemon juice, sugar, zest, eggs and butter; bring to a quick boil whisking constantly, then add the gelatin.

Trim the cake into two identical squares; line the pan with plastic wrap, lay in one square, spread the marmalade evenly, cover with the second square and freeze.

Smooth the chilled lemon custard, split it in half and fold whipped cream into one half. Pipe small uneven balls of lemon custard and of the lemon chantilly on top.

Freeze completely, unmold and cut into 11 bars or serve whole; garnish with mandarin supremes and thin strips of candied orange peel.