Preheat the oven to 375°F. Line a large baking sheet with parchment paper.
Pat the 6 bratwurst links dry with a paper towel. Slice each sausage into thirds to create 18 short, thick segments.
Unroll the crescent 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 (you can bake the remaining two as regular crescent rolls).
Using a pizza cutter or sharp knife, slice each of the 6 large triangles lengthwise into 3 smaller triangles (giving you 18 small triangles total).
Place a thick piece of sausage at the wide end of each small dough triangle and roll it up toward the point.
Place the wrapped bite seam side down on the prepared baking sheet. Continue with the rest of the sausages and dough, leaving about 1 inch of space between each bite.
Lightly brush the tops of the wrapped bites with melted butter.
Bake for 12 to 15 minutes, or until the crescent dough is puffed and golden brown.
Allow to cool on the baking sheet for 3 minutes before transferring to a serving platter. Serve with mustard for dipping.