Break the chocolate into pieces and melt in a hot water bath. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease two tart moulds (each approx. 15 cm Ø; alternatively a round springform pan, 26 cm Ø).
Cream 150 g butter, sugar and 1 pinch of salt with the whisks of the mixer. Stir in the eggs one by one. Stir in about half the chocolate. Mix flour, baking powder and cocoa. Alternately stir the cocoa into the butter-sugar-chocolate cream.
Spread the dough into the moulds and smooth it down. Bake in a hot oven for approx. 30 minutes (stick test).
Let the cake cool down. If necessary, melt the rest of the chocolate in a hot water bath again. Spread it on the cakes as a glaze. Immediately sprinkle with popcorn and let it set.