spaghetti with broccoli cream pesto

INGREDIENTS

• 1/2 pound broccoli
• 1/2 pound dried spaghetti
• 1 tablespoon unsalted butter
• 1 tablespoon olive oil
• 1/2 small onion, finely chopped
• 1 clove garlic, minced (or, more to taste)
• 1/2 teaspoon table salt
• Freshly ground black pepper or pinches of red pepper flakes
• 4 tablespoons heavy cream
• A heap of grated parmesan (about 1/2 cup), to serve