Savory Bubble Buns

Place water in bowl of stand mixer and sprinkle yeast over. Let stand until bubbly, 5 to 10 minutes. Stir in butter, sour cream, sugar, egg and vanilla. Beat in 2 cups of flour, the salt and baking soda until incorporated. Add remaining flour and continue to mix until a smooth, soft dough forms.
Knead dough until smooth, using the dough hook attachment, about 2-3 minutes. Cover with plastic wrap. Let rise in a warm place until doubled in size, about 1 hour.
Grease a 12-cup muffin pan or line with muffin cups. Roll dough into a long cylinder and then divide into 12 equal portions. Divide each of the 12 portions into 4 equal pieces and roll each piece into a ball.
For each bun, coat four balls with melted butter and then roll them in a bowl of seasoning. Arrange three balls in the bottom of a prepared muffin cup. Using your fingertip, make a small well in the center and press in the fourth ball. Repeat with remaining dough and muffin cups.
Cover buns loosely with plastic wrap and let rise in a warm place until puffy and have doubled in size, about 40 minutes.
Preheat oven to 350°F. Bake buns until golden, 20-22 minutes. Let cool in pan. Use a knife to help remove buns from pan.