In the bowl of a mixer add three cups of Bisquick and two teaspoons of instant yeast. Mix to combine and stir in three tablespoons of softened butter.
In a glass measuring cup, combine two-thirds of a cup of milk, one-third cup of warm water, two large room temperature eggs, and three tablespoons of honey. Add the wet mixture to the dry ingredients.
Attach the kneading hook to the mixer and mix at low speed, scraping the sides of the bowl as needed. Increase the speed to medium. Knead for six minutes. The dough should feel a little sticky. If you feel the dough is sticking to the sides of the bowl too much, add a little Bisquick until the dough pulls away. Don't add too much Bisquick, or the buns may turn out dry.
Continue kneading for an additional two minutes.
Remove the dough from the bowl and form it into a ball. Place it into a lightly greased, covered bowl, and let rise in a warm place for two hours, or until doubled in bulk.
Transfer the soft dough onto a Bisquick floured surface. Sprinkle a little Bisquick on top as well. Divide the dough into eight equal parts. Form each piece into balls and place on a lightly oiled parchment-lined baking sheet. Arrange two inches apart on the baking sheet, as they will rise a little more.
Flatten the balls down a bit, and brush each one with a bit of the beaten egg yolk. Sprinkle the caramelized onions and some sesame seeds over the top. Cover loosely with oiled plastic wrap and let the buns rise in a warm place for an additional hour, or until they appear puffy.
Preheat the oven to 400°F, with the rack positioned in the center of the oven. Turn sheet halfway through baking. Bake until the tops are golden brown, about twelve minutes.