In an 8-inch cast iron skillet, cook bacon over medium heat, stirring occasionally, until bacon is browned and crisp, about 10 minutes. With a slotted spoon, remove from skillet and drain on paper towels.
Add onions to skillet with the bacon drippings. Sprinkle onions with sugar and salt. Reduce heat to medium-low. Cook for 25 minutes or until onions are tender and golden, stirring occasionally, and adding the garlic the last 2 minutes of cooking.
Preheat oven to 375°F.
In a medium bowl, stir together cheese, sour cream, mayonnaise, and 1 teaspoon thyme until well combined. Stir into the caramelized onions in the skillet, along with 3/4 of the bacon. Top with the remaining bacon. Bake about 20 minutes or until mixture is bubbly. Cool slightly. Sprinkle with additional thyme before serving.
Serve with thick-cut cucumber slices and/or toasted slices of French bread.
Tip: If you don't have an 8-inch cast-iron skillet, spoon mixture into a 1-quart round casserole dish. Bake as above.