Combine first 4 ingredients in a small, heavy saucepan over medium heat. Heat to 180° or until tiny bubbles form around edge (do not boil). Remove from heat; let stand 15 minutes. Strain milk mixture through a sieve into a bowl, reserving milk. Discard solids. Wipe pan clean with paper towels; add strained milk and flour to pan, stirring with a whisk. Return pan to medium heat; cook 2 minutes or until thick, stirring constantly with a whisk. Remove from heat. Add cheeses, salt, and pepper, stirring with a whisk until smooth. Keep warm.
Cook broccoli in boiling water 3 minutes or until crisp-tender; drain. Top with cheese sauce; serve immediately.