Halve the sausages lengthways. Take the dough out of the tin, unroll and cut into 6 triangles. Brush with mustard. Sprinkle with 1 teaspoon of fried onions and 1 piece of sausage on top. Roll up from the short side.
Place the sausage croissants on a baking sheet lined with baking paper. Bake in the oven at 200 degrees (convection: 175) for 12-15 minutes until golden brown.
Mix egg yolks and condensed milk. Brush the croissants with it approx. 5 minutes before the end of the baking time. Scatter the rest of the fried onions over the top, press down a little.