Cook onion in butter and olive oil over medium low heat until caramelized, about 20 minutes.
Slice rolls in partially in half lengthwise, like a hot dog bun, not cutting all the way through, forming a pocket.
Spread mustard on the inside and top with a few caramelized onions and 1 smokie.
Place buns on a baking sheet and bake at 350 for 15-20 minutes until heated through.
Makes 20 mini dogs.