Lightly beat egg yolks; mix with sour cream and flour. Beat egg whites until stiff; fold into sour cream mixture.
In a baking dish, about 12 x 7-inches, layer half of the zucchini, half of the sour cream mixture, and half the cheese; sprinkle with bacon. Repeat layers of zucchini, sour cream mixture, and cheese. Combine crumbs and butter; sprinkle over the top of the casserole.
Bake, uncovered, at 350 degrees for 20 to 25 minutes.
Serves 6 to 8.