Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease the mould with butter and dust with flour.
For the topping, briefly blanch the apricots with hot water. Skin, halve and stone the fruit.
For the sponge mixture, mix 225 g flour with baking powder and sieve into a mixing bowl. Finely dice the marzipan. Add 225 g butter, icing sugar, vanilla sugar, lemon zest and eggs to the flour. Mix everything with the whisks of the mixer, first on a low setting, then on the highest setting, to a dough that falls off the whisk with a hard tear.
Fill the dough into the prepared springform pan and smooth it down.
Spread the apricot halves with the round side down in a circle on the dough and press them in gently.
Bake the cake in a hot oven on the middle shelf for 40-45 minutes. Remove from the oven and allow to cool completely on a cake rack. Remove from the tin.
Warm the apricot jam in a small pot. Spread the cake including the edge. Sprinkle with pistachios.