Preheat the oven to 325 degrees F. Spray a 15-cup bundt pan with with nonstick baking spray OR use a pastry brush to coat the pan in butter and add 2-3 tbsp of flour. Coat the entire pan in the flour and tap off any excess flour. Set aside.
Start by mixing the dry ingredients - In a separate bowl, add cake flour, nutmeg, cardamom, and kosher salt together in a bowl. Whisk together and set aside.
Add butter, butter flavored shortening, and sugar to the bowl of a stand mixer fitted with the paddle attachment. Mix on medium speed for 7 minutes, scraping down the sides of the bowl midway through. Begin adding eggs, one at a time, ensuring that each egg is fully incorporated prior to adding the next. Then add in the vanilla extract and butter vanilla emulsion. Scrape down the sides of the bowl again and continue to mix for 1-2 minutes, until all ingredients are fully incorporated and the mixture looks fluffy.
Add half of the flour mixture to the bowl, mix until just combined, about 15 seconds. Then pour in the buttermilk and continue to mix on low speed until combined, about 10 seconds. Add the remainder of the dry ingredients and mix until combined, about 20 seconds.
Scrape down the sides of the bowl once more, ensuring to scrape all of the way down to the bottom of the bowl, making sure that all of the batter is mixed together.
Add the cake batter to the prepared bundt pan. Bake for 1 hour and 25-35 minutes, until a skewer inserted into the center of the cake comes out clean. Allow the cake to cool in the pan for 10 minutes, then turn over to cool completely on a wire rack.
Once the cake has cooled, make the powdered sugar glaze by mixing together powdered sugar, buttermilk, sour cream, vanilla extract, a pinch of salt, and the tiniest dash of cardamom. Pour on top of the cake and serve.
Notes
Use room temperature ingredients - this applies to the butter, shortening, eggs, and buttermilk. Using room temperature ingredients creates a smooth batter that traps air when mixed, leading to a lighter, fluffier texture in cakes. Cold ingredients can cause uneven mixing and may prevent proper emulsification, which can affect the cake's structure and rise.
Sift Dry Ingredients: Sifting flour, and spices ensures a lump-free batter and a finer crumb texture.
Grease the Pan Thoroughly: Coat your bundt or donut pan with butter and flour (or baking spray with flour) to prevent sticking and ensure clean edges.
Store Properly: Keep the cake covered or in an airtight container to maintain its moisture and freshness for up to a week.
Cool Before Unmolding: Let the cake cool in the pan for 10–15 minutes before turning it out onto a rack to avoid breaking or sticking.