Cook the bacon until crispy (I baked mine at 400 degrees for about 15 minutes). Reserve three tablespoons of the bacon grease. Set aside the bacon on a paper towel and crumble.
in a saucepan, cook the garlic in ¾ cup of beer until the garlic is fragrant. Mix ¼ cup of the remaining beer with the cornstarch and lemon juice to make a slurry. Add this to the hot beer mixture.
Add the cheese, one cup at a time and mix until melted. stir in the mustard, the bacon grease, and ¾ of the crumbled bacon. Transfer to a serving bowl and top with the remaining bacon.
Serve warm.
Notes
Take your time adding the cheese and stirring. It can very easily become grainy in texture. Do not overheat the mixture and stir until just combined and the cheese is fully melted.