Boil a large pot of salted water over high heat. Add pasta and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté for 3-4 minutes until translucent. Stir in minced garlic and sauté for an additional 1-2 minutes.

Lower heat to medium-low, add heavy cream, and stir continuously. Gradually add grated pepper jack cheese and stir until melted and creamy, about 3-4 minutes.

Sprinkle in chili powder and black pepper to taste, stir to combine, adjusting seasoning as necessary.

Add drained pasta to the skillet and use tongs to toss until thoroughly coated. Incorporate reserved pasta water if sauce is too thick.

Serve immediately, garnishing with fresh herbs or additional cheese if desired.