1.
Cream the butter. Add sugar, vanilla sugar, salt, milk, and cocoa and beat until the mixture is light. Fold in the flour.
2.
Chill the dough for about 30 minutes.
3.
Divide the dough in half and shape two rolls about 3–4 cm in diameter. Wrap in cling film and chill again for 30 minutes.
4.
With a sharp knife cut slices about 4 mm thick and place on a baking tray lined with baking paper.
5.
Bake in the preheated oven at 200°C in the middle for about 10 minutes. Place on a rack and let cool.
6.
Spread raspberry jam on one cookie each and place a second one on top.
7.
Melt the chocolate in a bain-marie. Dip the sablé sandwiches halfway and let dry.