- Trim bottoms of broccoli stems and cut off broccoli heads; cut the broccoli heads into quarters. Peel broccoli stems and cut into quarters crosswise.
- Bring a large pot of lightly salted water to a boil; reduce heat to medium and cook broccoli until tender when cut with a paring knife but still slightly firm, 5 to 6 minutes.
- Transfer broccoli to a large bowl filled with cold water and chill to stop the cooking process. Drain well. Arrange broccoli in a colander with the florets facing down towards the holes of the colander and allow broccoli to drip for at least 30 minutes.
- Whisk together garlic, lemon juice, rice vinegar, Dijon mustard, red pepper flakes, salt, and black pepper together in a large serving bowl. Slowly drizzle in olive oil while whisking rapidly until the dressing is thick and creamy. Adjust salt, black pepper, and crushed red pepper flakes to taste.
- Toss broccoli with the dressing; let stand 5 to 10 minutes to marinate, then toss again. Can be refrigerated up to an hour if you want to serve the salad cold.