Start by slicing the onions into even, ¼-inch slices.

Heat the butter and olive oil in a medium skillet over medium heat. Add the onions and toss to coat. Allow them to caramelize for 40-50 minutes, stirring every few minutes. If they cook too quickly, reduce the heat. Once caramelized, remove and set aside.

While the onions are cooking, cut the bacon into thirds for even cooking. Add them to a large, high-walled skillet over low heat and cook until crispy on each side. Tip: Measure out the other ingredients while the bacon cooks.

Remove the bacon and set it on a paper towel-lined plate. Reserve 4 tablespoons of bacon drippings, or use butter if you don’t have enough drippings.

Boil salted water for the pasta shells at this point.

Heat the reserved bacon drippings in the skillet over medium heat. Whisk in the flour and stir continuously for 2 minutes.

Gradually add the heavy cream in splashes, stirring to prevent breaking the roux. Add the milk in the same manner.

Stir in the mustard powder, thyme, garlic powder, and hot sauce. Bring the mixture to a boil, then reduce to a simmer.

Cook the pasta until just al dente, according to package instructions, and then drain.

Lower the heat of the sauce and let it cool slightly. Gradually sprinkle in the cheeses, stirring continuously until melted and incorporated.

Mix in the caramelized onions and drained pasta using a silicone spatula until well combined.

Roughly chop the bacon and sprinkle it over the mac and cheese. You can stir some in if you’d like.

Garnish with parsley and serve hot!