Cook bacon in a large skillet over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain on paper towels; reserve drippings in skillet. Crumble bacon.

Melt butter in the same skillet over medium heat. Add onion, celery, and garlic; cook until tender and lightly browned, about 15 minutes. Transfer vegetables and bacon to a large bowl; stir in mashed potatoes, cheese, flour, egg, mustard, black pepper, and hot sauce to combine.

Heat vegetable oil in the same skillet over medium heat. Drop potato mixture by spoonfuls, flattening slightly; cook until golden brown on both sides, 5 to 7 minutes. Serve with sour cream.