Preheat your oven to 350°F (175°C). Butter your baking dish and set it aside. This is also a great time to warm your milk (microwave or stovetop) – warm milk mixes better with the roux.
Cook the pasta in salted water until just shy of al dente (about 1-2 minutes less than package directions). It'll continue cooking in the oven, and nobody likes mushy mac. Drain and set aside.
In a large skillet, cook the chopped bacon over medium heat until crispy, about 8-10 minutes. Remove with a slotted spoon to a paper towel-lined plate, but leave that gorgeous bacon fat in the pan. (Save about 2 tablespoons of the cooked bacon for topping later.)
Make the roux. Add the 4 tablespoons of butter to the bacon fat in the skillet. Once melted, whisk in the flour and cook for about 1-2 minutes until it smells slightly nutty but hasn't browned.
Slowly whisk in the warmed milk and cream, continuing to whisk until smooth. Cook this mixture, stirring constantly, until it thickens enough to coat the back of a spoon, about 5-7 minutes.
Turn heat to low and add cheeses. Stir in 3 cups of the grated cheddar and all of the cream cheese until melted and smooth. (Save 1 cup of cheddar for topping.)
Add the flavor bomb. Mix in the drained pimentos, garlic powder, onion powder, cayenne, smoked paprika, Dijon mustard, and most of the bacon (remember, we're saving some for the top). Season with salt and pepper to taste.
Combine the sauce with the pasta, folding gently until all the pasta is coated. Pour this heavenly mixture into your prepared baking dish.
Top it off. Sprinkle the remaining cup of cheddar over the pasta. Mix the panko with the melted butter and scatter over the cheese. Finally, sprinkle the reserved bacon on top.
Bake for 25-30 minutes until bubbly around the edges and the top is golden brown. If you want an extra-crispy top (and who doesn't?), broil for 1-2 minutes at the end – but watch it closely!
Rest for 5-10 minutes before serving. Garnish with sliced green onions and prepare for the compliments.