Grease a round springform pan (26 cm Ø), dust with flour and chill. For the dough mix 250 g flour with baking powder. Add sugar, egg and 150 g butter in pieces. Knead first with the dough hooks of the mixer, then with your hands briefly to a smooth dough.
Roll out the dough on a little flour and make it round (about 30 cm Ø). Line a mould with the dough, forming a 4-5 cm high rim and press it on. Put the springform pan in a cool place for about 1 hour.
For the filling, cut the marzipan into slices and press each one flat. Place on the cooled dough base. Refrigerate the mould again.
Meanwhile heat poppy seeds, 1⁄2 l milk, butter in pieces, sugar and semolina in a pot while stirring with a whisk. Stir starch with 100 ml milk until smooth. Stir into the hot poppy milk. Heat for another 3-5 minutes while stirring until the mixture is very slightly creamy.
Don't worry, it'll be much firmer in the oven. Take it off the stove. Whisk the egg and quickly stir it into the mixture. Preheat the oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Pour the poppy seed mixture into the mould and bake in the hot oven for approx. 1 hour.
Remove and let it cool down.
For the meringue, whisk the egg whites and icing sugar with the whisks of the mixer until smooth, then beat at the highest setting for approx. 10 minutes to a shiny, firm mass. Remove the poppy seed cake from the tin and place on a cake plate.
Spread the egg whites loosely over the cake. Scorch with a kitchen gas burner.