Stir in cheese and seasoning:
Reduce heat to low and stir in the shredded cheddar and Gruyere cheeses until fully melted and smooth. Add the mustard powder, garlic powder, salt, and pepper. Taste and adjust seasoning as needed. The sauce should be bold, savory, and slightly tangy with depth from the beer.
Combine pasta and bacon:
Fold the cooked macaroni into the cheese sauce until fully coated. Add most of the crumbled bacon, reserving a small handful for topping. Mix gently to distribute evenly.
Assemble and bake:
Pour the mac and cheese mixture into the prepared baking dish, spreading evenly. Sprinkle the reserved bacon on top for added crunch and flavor. Bake in the preheated oven for 20 to 25 minutes, or until the edges are bubbling and the top is golden brown.
Garnish and serve:
Remove the dish from the oven and let it rest for 5 minutes. Garnish with chopped fresh parsley just before serving for a pop of color and freshness.
