1. Bring a large pot of salted water to a boil and add the broccoli florets. Blanch for 2 to 3 minutes, until bright green and just tender, then drain well and set aside.

2. In a large skillet, melt the butter with the olive oil over medium heat. Add the minced garlic and cook for 30 to 60 seconds, stirring often, until fragrant and lightly golden but not browned.

3. Pour in the chicken broth, stirring to deglaze the pan, and let it bubble for about 1 minute. Stir in the heavy cream, kosher salt, black pepper, and crushed red pepper flakes if using.

4. Simmer the sauce gently for 2 to 3 minutes, stirring frequently, until slightly thickened and able to coat the back of a spoon.

5. Reduce the heat to low and stir in the grated Parmesan until fully melted and the sauce is smooth and creamy. Add the lemon zest and adjust seasoning to taste.

6. Add the blanched broccoli to the skillet, tossing gently to coat every floret in the garlic Parmesan sauce. Cook for another 1 to 2 minutes, just until the broccoli is heated through.

7. Transfer the broccoli and sauce to a serving dish. Top with the shredded Parmesan and sprinkle with chopped parsley before serving.