Fry diced bacon until crisp. Remove and drain. Saute chopped onion in bacon drippings until tender, but do not brown. Set aside.
Sift together flour, baking powder, baking soda, and salt in a large mixing bowl.
Combine beaten eggs, milk, and sour cream in a small bowl; blend well. Add at once to dry ingredients, stirring just enough to moisten. Stir in bacon and sauted onion. Spoon batter into greased muffin tins, filling two-thirds full. Sprinkle with sesame seed.
Bake in a 375*F oven for 18 to 20 minutes or until golden brown.
Remove from oven. Let completely cool.