Preheat oven to 400 degrees. Line a baking sheet with foil or parchment paper.
Place tomatoes, onions, and garlic cut side up on the baking sheet.
Drizzle with olive oil and season with salt and pepper. Place the head of garlic into a small piece of tin foil and wrap it tightly, sealing the garlic inside.
Roast veggies for 50 minutes.
While the veggies are roasting, make the spaghetti.
Carefully transfer roasted tomatoes and onions to a blender. Squeeze garlic from its skin and into the blender. Add all the juices from the sheet pan as well.
Add fresh basil and blend until smooth.
Heat in a medium saucepan over medium heat until warmed through.
Remove from heat and stir in heavy cream.
Season to taste with salt and pepper. Serve with spaghetti or the noodle of your choice, garnish with Parmesan and enjoy!
