Cook bacon in a large skillet over medium-high heat 8 to 10 minutes or until crisp.
Drain on paper towels and then crumble. Melt butter with oil in a large sauté pan over medium-high heat. Add the sliced onions, sugar, and salt; stir occasionally – cook about 10 minutes or until onions soften and just begin to turn golden. Reduce heat to medium and continue to cook, stirring often, 20 minutes or until onions turn deep golden brown. Stir in the sherry vinegar, to deglaze pan. Continue to cook until vinegar is reduced by half and add the thyme.
Combine the cheese, sour cream, mayo & black pepper in a medium bowl. Stir in onions & bacon and transfer to a heat proof baking dish.
Bake in a 400 degree oven for about 20 minutes or until mixture bubbles and top is lightly golden.
Serve with crusty bread, crackers or veggies for dipping.
