Preheat oven to 220°C. Line a large baking tray with baking paper.
Roll the pastry out on a floured work surface into a 3-mm thick round. Use a sharp knife or pastry cutter to cut the round into 12 triangular slices, like you're dividing up a cake.
Use a sharp paring knife to make an incision, about 2.5 cm deep, in the centre of the wedge opposite the tip. Pull the dough apart slightly to widen the incision.
To make the filling, slice the meats and gherkin into small pieces or fine strips; combine.
Centre a dollop of filling at the wide end of each slice and then gently roll up the dough, letting the very tip peek out from under the croissant. Bend the ends gently to form crescent shapes, then place them on the baking tray. Chill for 20 minutes.
Mix the cream with 2 tablespoons of water and brush over the croissants. Bake for 10–15 minutes until golden brown. Cool briefly on baking tray; serve lukewarm.