In a large pot, bring salted water to a boil. Add the broccoli florets and blanch for 2-3 minutes until bright green and slightly tender. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it.
Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan cheese, salt, black pepper, and red pepper flakes (if using). Continue stirring until the cheese is melted and the sauce is smooth.
Add the blanched broccoli to the skillet and toss to coat in the creamy sauce. Cook for an additional 2-3 minutes until the broccoli is heated through.
Remove from heat and stir in the lemon juice. Taste and adjust seasoning if necessary.
Serve warm, garnished with chopped parsley if desired.