Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 425 degrees. Bring a large pot of salted water to a boil. Wash and dry produce. Cut broccoli florets into bite-size pieces, if necessary. Peel and mince or grate garlic.

Toss broccoli on one side of a baking sheet with a drizzle of olive oil; season with salt and pepper. Place bacon on empty side. (For 4 servings, divide between 2 sheets; roast bacon on top rack and broccoli on middle rack.) Roast on top rack until broccoli is tender and bacon is crispy, 15-20 minutes. (TIP: If bacon is done before broccoli, remove from sheet and continue roasting broccoli.) Once bacon is cool enough to handle, chop into bite-size pieces.

While broccoli and bacon roast, add spaghetti to pot of boiling water. Cook until al dente, 9-11 minutes. Reserve 11/2 cups pasta cooking water (2 cups for 4 servings), then drain.

Once broccoli and bacon are done, melt 1 TBSP butter in pot used for pasta over medium heat; add garlic and cook until fragrant, 30 seconds. Add cheese roux and 1 cup reserved pasta cooking water (11/2 cups for 4 servings); whisk to combine. Cook, whisking, until slightly thickened, 2-3 minutes. Reduce heat to medium low and whisk in cream cheese to combine.

Add drained spaghetti, 1 TBSP butter (2 TBSP for 4 servings), and half the Parmesan (save the rest for serving) to pot with sauce. Cook, tossing, until pasta is coated in a creamy sauce, 1-2 minutes. (TIP: If necessary, stir in more reserved pasta cooking water a splash at a time.) Taste and season with salt and pepper.

Stir bacon and broccoli into pasta, then divide between plates. Sprinkle with remaining Parmesan and serve.