For the bread bowl: Preheat the oven to 375 degrees F.
Remove the top quarter of the bread round, then cut it into cubes and set aside. Using a knife, cut out the interior of the bread round, leaving it hollow. Cube the removed bread and set aside.
Mix together the olive oil, garlic and red pepper flakes in a small bowl. Brush the outside and inside of the bread bowl with the oil mix. Place the bread bowl on a sheet pan and sprinkle the inside with the Parmesan. Toss the cubed bread in the remaining oil and place on the sheet pan next to the bread bowl. Bake until crisp, 15 to 18 minutes.
For the beer cheese: Meanwhile, add the butter to a large saucepan or high-sided skillet over a medium heat. When the butter has melted, add the onions, garlic and red pepper flakes, then cook until the onions are golden, 8 to 10 minutes. Sprinkle over the flour and stir to combine. Slowly pour in the milk and beer a little at a time, whisking until smooth after each addition. Add the mustard and cheeses and stir until smooth.
Pour into the crisp bread bowl and serve alongside the bread cubes, pretzel rods, carrots and celery.