Preheat oven to 425°F. Line a baking tray with parchment paper.
Remove chorizo sausage from casing. In a large mixing bowl add chorizo, butternut squash, salt, pepper, garlic, sage and onions. Mix until fully combined.
Whisk egg yolk and water in a small bowl, set aside.
Working in batches, roll out 1 block of puff pastry on a lightly floured work surface into a 9in x 12 in rectangle. Slice in half lengthwise. Place ½ cup of mixture along the edge of the long side of pastry and press into a sausage shape. Repeat with second pastry piece.
Roll pastry up over mixture and roll into a sausage shape leaving ¼ inch boarder at the top. Brush some egg wash onto the pastry and continue to roll to seal pastry. Slice roll into 4, 2-inch pieces.
Transfer rolls onto lined baking tray seam side down and brush with egg wash. Top with some salt and sesame seeds. Bake for 20-25 minutes, until puffed and golden brown.
Repeat steps with remaining pastry and butternut chorizo mixture.
Mix Dijon mustard and maple syrup together and serve with sausage rolls.
You can freeze unbaked sausage rolls. Wrap well and keep for another meal.