Heat oven to 180C/160C fan/gas 4. Line a 20 x 30cm baking tin with baking parchment. Unroll the croissant dough and squeeze the perforated lines back together. Use a pizza cutter to cut the dough into 2cm thick strips, working across from one of the shorter edges. Roll each strip and place, swirl-side up in the tin. Arrange the rolls randomly.
Melt the butter with the rosemary and pour it over the rolls. Bake for 40 mins until golden brown. Serve with your favourite dips.