First, preheat your oven to 350℉. Melt Butter in a small saucepan on the stovetop. I like to brown my butter. This takes about five minutes on medium-low heat. Watch it carefully. When it starts to look golden and smell nutty, remove it from heat and let it cool. I butter my pan taking the time to get in all the nooks and crannies of the Bundt pan. Then I take 1/4 cup of flour and sprinkle it into the pan, knocking the outside of the pan and rotating to get an even layer of flour over the butter.
Peel and chop your apples. You can slice or chop them finer or rough chop, you could even grate your apples! I slice mine in 1/4 pieces. Just know you'll get a different texture throughout the cake depending on how you decide to do this.
Mix wet ingredients. Cream your oil, sugar, cooled brown butter, and eggs together in a large bowl. Then add sour cream, and sourdough starter (the sourdough starter is optional). Mix with a whisk until smooth
Mix dry ingredients. Into your medium-sized bowl sift flour, salt, baking powder, baking soda, and cinnamon.
Add flour mixture to wet ingredients and with your spatula mix and scrape the sides of your bowl until just combined and no more flour is present.
Add chopped apples and any of the optional ingredients.
Pour batter into pan and smooth
Bake the cake in the oven on the middle rack at 350℉ for 40 minutes, checking after 30 minutes for doneness. The cake will be golden on the outside and a toothpick will come out clean from the center.
When you are sure it is done, remove it from the oven and place it on a cooling rack. Please be patient and let it cool completely before removing the cake from the Bundt Pan.
Turn your cake out onto a cutting board and cut into 2-3 inch slices. I like to sprinkle confectioner sugar with my sifter over the apple cake slices. Enjoy!