First, add the sugar, oil, and egg to the mixing bowl and mix for 1 min / Speed 5.
260 g All-purpose flour, 180 ml Buttermilk, 1 tsp Baking powder (level), ½ tsp Salt, ½ tsp Baking soda
Add the remaining batter ingredients—flour, baking powder, baking soda, salt, and buttermilk—and mix for another 30 sec / Speed 5.
Divide the batter evenly among the 12 muffin cups.
50 g Brown sugar, 1 tsp Ground cinnamon, 30 g Butter, cubed, pinch Ground nutmeg
Rinse out the mixing bowl, add all the ingredients for the cinnamon swirl, and melt for 2 min / 50 °C / Speed 2.
Spoon 1 teaspoon of the cinnamon mixture onto each muffin, then gently swirl it into the batter using a toothpick or small teaspoon.
Bake on the lower rack for 20–25 minutes. (Toothpick test: Insert a toothpick into the center—if it comes out clean with no wet batter, they are done!)
60 g Sour cream (or crème fraîche or cream cheese), 20 g Powdered sugar
For the glaze, stir the sour cream and powdered sugar together until smooth and spread over the muffins. Dust with a touch of cinnamon and serve!