Place <quantity>500<unit>g</unit></quantity> of puff pastry dough on a floured surface and roll it into a <quantity>30<unit>cm</unit></quantity> x <quantity>20<unit>com</unit></quantity> rectangle

Place the dough rectangle on top of a piece of parchment paper and roll it onto itself. Make sure only the parchment paper is in contact with the puffed pastry

Place the dough in the refrigerator until it is time to use it

Trim, halve, and peel <quantity>1</quantity> onion

Small dice the onion

Pick the leaves out of <quantity>1</quantity> small bunch of sage, and thinly slice them

Melt <quantity>1<unit>tbsp</unit></quantity> of butter on a skillet over medium heat

Add the diced onion and sage. Cook until translucent and remove from heat

Remove the casings of <quantity>500<unit>g</unit></quantity> of beef sausages and place the meat on a bowl

Add the sautéed onions with sage, and <quantity>½<unit>tsp</unit></quantity> of Dijon mustard

Add salt and ground black pepper to taste

Mix until everything is incorporated

Dust all-purpose flour over a working surface. Divide the seasoned meat into <quantity>3</quantity> parts and roll each part into a <quantity>30<unit>cm</unit></quantity> long cylinder

Crack <quantity>1</quantity> egg into a bowl and add a pinch of salt

Beat the egg until homogeneous

Remove the dough from the refrigerator and roll it open on a working surface. Trim off the rough edges

Place <quantity>1</quantity> sausage on top of the dough, <quantity>2<unit>cm</unit></quantity> away from the edge. Brush around <quantity>4<unit>cm</unit></quantity> of the other side with the egg mixture and fold over

Cut it on the end of the fold and seal the pastry together by pressing it with a fork. Repeat the process with the other sausages and the remaining dough to create <quantity>2</quantity> more rolls

Brush an even layer to the egg mixture on top of the rolls

Transfer the rolls to the refrigerator for 30m to firm up

Preheat the oven to <temperature>200<unit>°C</unit></temperature> with the fan on

Remove the rolls from the refrigerator and gently score the top of them with a knife

Bake the rolls for 30-40m until fully cooked and perfectly golden brown on the outside. The sausage rolls are ready

Enjoy! It is amazing!