Line 12 muffin cups with paper liners. Put room temperature egg whites in medium all metal or glass bowl with cream of tartar and beat at high speed until foamy. Add sugar, 2 tablespoons at a time, beating until whites hold stiff glossy peaks.
Add lemon juice and flour.
Fold in with a spatula until blended.
Fold in coconut.
Spoon into the lined muffin cups. Bake 30 to 35 minutes. Cool on a rack.