Bring a large pot of salted water to a boil. Add the pasta and cook until al dente, about 8-10 minutes. Drain and set aside, saving a cup of pasta water.
Heat a large sauté pan over medium-high heat. Add sliced sausage or pepperoni and cook until crispy and browned, about 4-5 minutes, until sizzling and edges are crisp.
Pour in olive oil and add minced garlic along with red pepper flakes. Cook for about 30 seconds until fragrant, the garlic should turn golden and smell spicy and sweet.
Pour in heavy cream and stir well to combine. Let it simmer gently for about 2 minutes until the sauce starts to thicken and turn silky, with tiny bubbles forming around the edges.
Add the drained pasta into the pan with the sauce. Toss well to coat every strand, listening for the gentle clink of pasta against the pan and watching the sauce cling to the noodles.
Sprinkle shredded cheddar cheese over the pasta and stir until melted and gooey, creating a velvety, cheesy coating. If the sauce seems too thick, loosen it with a splash of the reserved pasta water.
Stir in grated Parmesan and squeeze fresh lemon juice for brightness. Finish with freshly cracked black pepper to taste, then give everything a final toss.
Serve immediately while hot, with extra cheese or herbs if desired. The sauce should be silky and cling to the pasta, with a slightly golden cheese top and a fiery, cheesy aroma filling the air.