Put flour, lemon zest and 1 tablespoon of sugar in a mixing bowl. Stir yeast and 1 tablespoon of sugar until the yeast becomes liquid. Pour into the flour. Melt the fat and add the cold milk.
Pour the lukewarm milk-fat mixture into the bowl and knead into a smooth yeast dough. Cover with a damp tea towel and leave to rise in a warm place for 15-20 minutes.
Knead the dough briefly and let it rise for another 15 minutes. Then form a roll from the dough and cut it into 12 large pieces. Form them into snails of about 8 cm Ø. Put them on a baking tray lined with baking paper.
Mix the egg yolk and 1 teaspoon of cream and spread it on the snails. Bake in the preheated oven (electric cooker: 175-200 ° C/ gas: level 2-3) for about 20 minutes. Let it cool down on a cake rack.
Whip cream and remaining sugar until stiff. Cut snails in half and fill each with a tablespoon of cream. Dust with icing sugar. Makes about 12 pieces.