Using a large skillet, add butter and olive oil. Place over medium heat until butter melts.

Add onions; cook, stirring occasionally, for 5-7 minutes, or until onions begin to soften.

Add sugar and salt; reduce heat to medium-low and continue cooking, stirring occasionally, for 10-15 more minutes, or until onions have softened and turned light golden brown. (Note: If the onions begin to scorch or stick to the bottom of the pan, turn the heat down. The secret to caramelized onions is low and slow!)

Using a small bowl, add all of the ingredients for the BBQ sauce; whisk together until well combined. Set sauce aside.

Using a small bowl, whisk together melted butter and Dijon mustard.

Brush the melted butter mixture onto the bottom side of each of the top buns.

Place rolls butter-side down in a large frying pan or griddle. Place over medium heat and cook until butter has fully melted and bottom of rolls have turned golden brown.

To make sliders, place bottom (untoasted) half of bun on countertop. Add several slices of fully-cooked smoked brisket, a spoonful of white sauce and a handful of caramelized onions. Top with lightly toasted buns.