Preheat the oven to 375°F (190°C). Line a large baking sheet with parchment paper.
Pat the bratwurst links dry with a paper towel. Slice each sausage into thirds to make 18 short pieces.
Unroll the crescent roll dough on a clean surface and separate it into its pre-cut triangles. You will only need 6 of the 8 large triangles for this recipe. Reserve the remaining two triangles for another use.
Using a pizza cutter or sharp knife, cut each of the 6 large triangles lengthwise into 3 smaller triangles, creating 18 pieces of dough.
Place one piece of sausage at the wide end of each small triangle and roll the dough toward the point.
Arrange the wrapped sausage bites seam-side down on the prepared baking sheet, leaving about 1 inch between each piece.
Brush the tops lightly with melted butter.
Bake for 12–15 minutes, or until the crescent dough is puffed and golden brown.
Let the bites cool on the baking sheet for 3 minutes before transferring them to a serving platter. Serve warm with mustard or beer cheese for dipping.
