To make the Sour Cream Yeast Dough:
Sprinkle the yeast over the water in the bowl of a stand mixer; set aside for 5 to 10 minutes until bubbly. Add the butter, sour cream, sugar, egg, and vanilla to the yeast mixture and stir to combine with a rubber spatula.
Attach the bowl to the mixer, and fit the mixer with the paddle attachment. Beat in 2 cups (9 ounces/255 grams) of the flour, the salt, and baking soda on medium-low speed until incorporated, 30 to 45 seconds. Add the remaining ½ cup (2¼ ounces/65 grams) flour and beat until a smooth, moderately soft dough forms.
Turn the dough out onto a lightly floured work surface and knead until smooth and satiny, about 3 minutes. At first the dough will be sticky. Add no more than 1 to 2 tablespoons additional flour during the kneading to combat the stickiness. Place the dough back in the bowl, cover tightly with plastic wrap, and let rise in a warm place (about 70 degrees F) until doubled in size, about 1 hour. The dough is ready when a finger gently pressed into it leaves an indentation. Meanwhile, prepare the pan and make the Cinnamon-Sugar Coating.
Center a rack in the oven and preheat the oven to 350 degrees F. Lightly coat a 12-cup standard muffin pan with nonstick spray, then flour the cups, tapping out the excess flour. Or, butter and flour the cups.
To make the Cinnamon-Sugar Coating:
In a small bowl, stir together the sugar and cinnamon; set nearby. Place the melted butter in a small, shallow dish.
To shape the buns:
Gently punch the dough down to deflate it. Form it into a long cylinder, and divide it into 12 equal portions (each portion is about 1¾ ounces/50 grams). Using kitchen scissors, a small metal spatula, or a dough scraper, divide I portion into 6 equal pieces, and then shape each piece into a ball. One at a time, roll the balls first in the butter and then in the cinnamon sugar. Arrange 5 balls next to one another in a circle in each prepared muffin cup, and then, using a fingertip, poke the sixth ball down slightly in the center.
Repeat with the remaining 11 dough portions. Loosely cover the buns with plastic wrap and set them aside in a warm place (about 70 degrees F) until puffy and doubled in volume, about 40 minutes. The dough is ready to bake when a finger gently pressed into it leaves an indentation.
Bake the buns until golden, 20 to 22 minutes. Transfer the pan to a wire rack and let cool for 5 to 8 minutes. Then tilt the pan and gently tap it on a counter to release the buns. If necessary, slip a knife blade between the pan and the bun to release. Transfer the buns to a wire rack.
To make the Translucent Vanilla Glaze:
In a small bowl, stir together the sugar, butter, milk, and vanilla until smooth and just the right consistency to apply a thin glaze over each bun. If it is too thick, add water, 1 teaspoon at a time.
The buns can be warm or at room temperature when you glaze them. Slip a sheet of waxed paper under the rack holding the buns to catch any drips. Using a pastry brush, coat each bun with the glaze. Serve the buns warm or at room temperature.