Add butter and olive oil to pan as it heats over medium heat.
Cook onions for 15-20 minutes until caramelized and nicely browned. Add vinegar and cook for an additional 1-2 minutes, then remove to dish.
Add bacon to pan and cook until crisp. While bacon cooks, grate the gruyere cheese and prepare yogurt and cream cheese.
Remove bacon to paper towel to blot. Drain excess oil from pan.
Turn down heat and allow pan to cool for a minute or two. Add grated cheese first (reserving some for garnish, if desired), followed by the yogurt, cream cheese and paprika. Stir to combine as they melt.
Once mixture is fairly gooey, add in the onions and crumble in about ⅔ of the bacon. Stir to combine, then remove to serving dish.
Bake @ 375° for 15-20 minutes. If desired, garnish with scallions, reserved cheese, and reserved bacon before serving.