In saucepan, bring 2 cups chicken broth and 2/3 cup long grain rice to boiling. Simmer, covered, 15 minutes. Remove from heat; let stand, covered, 10 minutes. Melt 3 tablespoons butter; stir in 3 tablespoons all purpose flour, 1 1/2 teaspoons salt, and dash pepper. Add 2 cups milk. Cook and stir till bubbly. Stir in 2 cups cubed cooked chicken, cooked rice, one 10 ounce package frozen chopped broccoli, cooked and drained, and one 4 ounce can sliced mushrooms, drained. Bake, covered, in 2 quart casserole at 350 degrees for 30 to 35 minutes. Top with 1/4 cup toasted slivered almonds. Serves 6.