Add the bacon to a sauté pan, and cook over med heat, until the bacon is crispy, about 5 min. Remove the bacon to a paper towel lined plate to drain, reserving 2 tablespoons of the fat in the pan
Return the pan to medium heat. Add the onions and sauté until the onions are soft and tender, about 10 minutes.
Season with salt and sugar then reduce the heat to medium-low and cook, stirring occasionally, until the onions are uniformly brown and caramelized, about 30 minutes.
Add the thyme and balsamic vinegar and remove the pan from the heat
Heat oven to 400ºF (200ºC). Combine cream cheese and sour cream in a medium mixing bowl or the bowl of a stand mixer.
Add the onions cheese & bacon
Add the caramelized onions, ¾ cup of the Asiago cheese, Cheddar cheese and the cooked bacon, stirring to combine.
Bake the dip
Spread the dip in a 9” (22cm) heat-proof baking dish and spread the remaining Asiago cheese over the top. Cook for 30 minutes or until hot and bubbly.
Serve the dip
Serve hot or at room temperature with crostini or buttery crackers.