3 1/4 cups of cake flour, sifted, plus more for dusting
1 tbsp. baking powder
1/2 tsp. baking soda
1 tsp. salt
1/2 tsps. ground cinnamon
2 sticks unsalted butter, softened
2 cups granulated sugar
1 1/2 tsps. orange zest, finely grated
4 large eggs, at room temperature
1/2 cups of sour cream, at room temperature
1 1/2 tsps. pure vanilla extract
1 1/4 cups buttermilk, at room temperature
confectioner's sugar, for dusting
Preheat the oven to 350 degrees. Spray three 8x4-inch loaf pans (disposable are fine) with vegetable oil cooking spray, dust with flour, and arrange them on a baking sheet.
In a medium bowl, whisk the cake flour with the baking powder, baking soda, salt and cinnamon. In the bowl of a stand mixer fitted with the paddle, beat the butter with the sugar and orange zest at medium-high speed until fluffy, about 4 minutes. Add the eggs one at a time, beating well between additions and scraping down the side of the bowl. Beat in the sour cream and vanilla. At low speed, beginning and ending with the dry ingredients, beat in the dry ingredients in 3 additions, alternating with 3/4 cup of the buttermilk; gently fold just until blended.
Scrape the batter into the prepared pans and smooth the tops; gently tap once to release any air. Bake the loaves for about 45 minutes, rotating the baking sheet halfway through, until a cake tester inserted in the center of each loaf comes out with a few moist crumbs attached.
Transfer the loaves to a rack for 20 minutes, then turn them out onto the rack and set them right side up to cool. Dust them with confectioner's sugar, slice and serve.
Notes: Can be made a day in advance.