11. Blanch broccoli florets in salted boiling water until bright green and slightly tender, about 2-3 minutes. Shock in ice water to stop cooking. Drain and set aside.
22. Melt butter in large heavy-bottomed stockpot over medium heat. Sauté diced onions until translucent and soft, about 4-5 minutes.
33. Sprinkle flour over onions, stirring constantly to create a blonde roux. Cook for 2 minutes to remove raw flour taste.
44. Gradually whisk in milk and chicken stock, ensuring no lumps form. Simmer and thicken for 5-6 minutes.
55. Reduce heat to low. Add heavy cream, grated cheeses, salt, white pepper, and nutmeg. Stir until cheese completely melts.
66. Fold in blanched broccoli florets. Simmer on low heat for 10 minutes to marry flavors.
77. Use immersion blender to partially purée soup, leaving some broccoli chunks for texture.