In the bowl of an electric mixer fitted with the dough hook attachment, stir yeast and 1/4 cup warm water. Let sit until the yeast comes alive and starts to foam, about 5-10 minutes. Stir in sour cream, butter, sugar, egg and vanilla.
Add 2 cups flour, salt and baking soda. Mix on low speed until all the flour has been incorporated, about 1-2 minutes. Add remaining flour, a little at a time, until the dough starts to come together. Knead on high speed until the dough gathers into a ball, about 2 minutes.
Cover with plastic wrap and let rise in a warm area until doubled in volume, about 1 hour.
Coat a 12-cup standard muffin tin with nonstick spray; set aside.
To make the cinnamon-sugar coating, combine brown sugar and cinnamon in a small bowl; set aside.
Gently punch the dough down to deflate it. Form the dough into a long cylinder, dividing it into 6 equal portions. Using a dough scraper, divide each of the 6 portions into 12 equal pieces, rolling each piece into a ball.
Dip each ball into the melted butter and then into the cinnamon-sugar mixture. Drop 5 coated dough balls into each muffin cup. Using your fingertips, gently press the 6th dough ball in the center.
Loosely cover with plastic wrap and let rise in a warm area until doubled in volume, about 40 minutes.
Preheat oven to 350 degrees F.
Place dough balls into oven and bake for 20-22 minutes, or until a tester inserted in the center comes out clean.
To make the glaze, combine confectioners’ sugar, butter, milk and vanilla. Whisk until smooth. If the glaze is too thin, add more confectioners’ sugar as needed.
When the cupcakes are done, cool for 10 minutes and drizzle the glaze on each cupcake.