Adjust an oven rack so that it is in the center of the oven. Heat the oven to 350° Butter and flour your Bundtlette pan. Melt butter in a large glass measuring cup and allow to cool.
Using your stand mixer (or hand mixer), whip the eggs and sugar on medium speed for 5-7 minutes or until the mixture become light yellow in color and fluffy. If using a stand mixer, you will use your whisk attachment for this.
While the eggs and sugar whip, combine cake flour, baking powder, baking soda, and salt in a medium mixing bowl.
Once butter has cooled to slightly warm, whisk together the butter, buttermilk, creme fraiche, orange juice, orange zest, and vanilla extract. This should be a nice, thick liquid. If you notice the butter is becoming lumpy, you can warm the mixture for 5-10 seconds in the microwave and whisk to dissolve the lumps.
Once the egg mixture is light and fluffy, gently fold the flour mixture into the egg mixture until combined. Do not over mix. Fold ⅓ of the butter mixture into the egg and flour mixture. Then fold the remaining butter mixture into the egg and flour mixture.
Fill the Bundtlette wells until about ¾ full. You will have leftover batter. You can either bake a second round of cakes and make 2 more, or you can bake the remaining batter in a 2 cup mini loaf pan.
Bake the cakes for 15-16 minutes or until a toothpick inserted into the center of one comes out clean. Be careful not to over bake these.
Remove the cakes from the oven and allow to cool for 10 minutes before turning them out of the pan onto a cooling rack.