Preparation

For the almond paste, cream the butter and sugar, using an electric hand mixer. Mix in the almonds, adding milk if too thick.
    
Cut the dough into 2 and roll half out on a floured surface to a 5 × 14 1/2in (12 × 36cm) rectangle. Cut into 3 × 5in (12cm) squares, then cut diagonally to make 6 triangles. Repeat with remaining dough.
    
Spread 1 tablespoon of the paste onto each triangle, leaving a 3/4in (2cm) border along the 2 longest sides. Brush the borders with egg. Roll the croissant up carefully from the longest side toward the opposite point.
    
Line 2 baking sheets with parchment paper and put the croissants on them. Cover and put in a warm place for 1 hour, until soft and spongy. Preheat oven to 425°F.
    
Brush the croissants with egg. Sprinkle with sliced almonds. Bake for 10 minutes, then reduce the temperature to 375°F. Bake for 5–10 minutes, or until golden. Cool. Dust with confectioner’s sugar to serve.