Cover the bottom of a small springform pan (approx. 20 cm Ø) with baking paper, enclose a rim around it and let it cool in the refrigerator for at least 2 hours.
Break chocolate into pieces. Warm the cream, remove from the stove. Melt the chocolate in it while stirring. Pour into the pre-cooled mould. Cover with foil and chill for at least 4 hours.
In the meantime, drain the cherries and collect the juice. Stir 4 tablespoons of juice and sauce powder until smooth. Boil up the rest of the cherry juice and sugar. Stir in the sauce powder. Simmer for 1-2 minutes.
Pour in the grappa, remove from heat, fold in the cherries. Let it cool down.
Stir the crème fraîche and milk until smooth. Loosen the rim with a knife. Turn the gateau out of the tin and remove the baking paper. Dust the gateau thickly with the cocoa. Serve with the grappa cherries and crème fraiche.