Melt two tablespoons of butter (either in the microwave or in a small saucepan). Toast the bread and then pulse the butter and bread together in a food processor until you have relatively small crumbs. Set aside.
In a large saucepan over medium heat, melt 6 tablespoons butter. Add flour and whisk constantly until combined and golden.
1/2 cup + 1 tablespoon unsalted butter, 2 Tablespoons all purpose flour
Add the evaporated milk and milk and whisk constantly until combined and relatively smooth. Add onion and garlic and stir for a few minutes until they've softened. Add ground mustard and whisk to combine. Salt and pepper to taste, then bring to a simmer.
1 12- ounce can evaporated milk, 1 cup whole milk, 1/2 cup onion, 1 Tablespoon garlic, 1 teaspoon ground mustard, Salt and pepper
Remove from heat, add cheddar and asiago cheeses and use a heat-resistant stirring spoon to combine until melted and smooth.
Add beaten egg and stir to combine. Taste test and add salt and pepper as needed.
1 egg, Salt and pepper
Add macaroni to the pan and stir to complete coat and combine.
Transfer to prepared baking dish and top with breadcrumbs.
Cover dish with foil and bake for 25 minutes. Remove foil and let broil for another 5 minutes until the breadcrumbs are golden and toasted.
Serve immediately and enjoy!
Notes
Storage: Once your baked mac and cheese has cooled to room temperature, transfer to an airtight container or tightly wrap the baking dish with plastic wrap or foil. Store in the fridge for up to 3 days.Freezing: Make sure the mac and cheese has completely cooled, and then portion out the dish into smaller servings (this will make it easier to reheat later). Place each section into airtight freezer-safe containers. Store in the freezer for up to 3 months.Reheating from fridge: Place the previously baked mac and cheese in an oven-safe dish and add about 1 tablespoon of milk to the dish for each cup of mac and cheese you’ll be reheating. Lightly cover the dish with aluminum foil and reheat at 350°F for about 20 minutes or until heated through.Reheating from freezer: Let the frozen mac and cheese thaw in the refrigerator for 24 hours, then follow the same steps as reheating refrigerated mac and cheese. Place the previously baked mac and cheese in an oven-safe dish and add about 1 tablespoon of milk to the dish for each cup of mac and cheese you’ll be reheating. Lightly cover the dish with aluminum foil and reheat at 350°F for about 20 minutes or until heated through.