Preheat oven to 400°. Cut a slit into the center of 18 pepperoni slices and place a slice into each hole of a muffin tin. Chop remaining 4 slices of pepperoni into small pieces.

In a large pot over medium heat, melt butter. Add flour and whisk until golden. Slowly pour milk in while whisking. Add heavy cream, garlic powder, and oregano. Season with salt and pepper. Bring to a simmer and cook for 2 minutes.

Add mozzarella and ½ cup of Parmesan and stir until cheese is melted.

In another large pot of boiling salted water, cook pasta until al dente, 7 minutes. Reserve about 1/2 cup of pasta water, then drain.

Add 2 tablespoons pasta water to cheese sauce and stir to combine. Add pasta and toss to coat. Add more pasta water as necessary to loosen sauce.

Spoon macaroni into pepperoni cups. Top with  about 2 tablespoons of Parmesan and chopped pepperoni. Bake until tops are golden and macaroni feels firm, 20 to 30 minutes.

Remove cups from tin and top with basil and remaining 2 tablespoons Parmesan before serving.