Preheat the oven to 350 F. Use baking spray to grease a 10 cup bundt pan.
In the bowl of a stand mixer, beat together the butter, coconut oil, salt, sugar, extracts and baking powder until very fluffy, at least five full minutes. If you are using a hand mixer beat longer.
With the mixer on, add an egg white one by one allowing each to fully be beaten in before adding another. Let the mixer beat for a few more minutes after all the eggs are incorporated. Scrape the bottom of the bowl in case any bits have gotten stuck.
Over the batter, sift in the cake flour. Using a rubber spatula, stir the flour in (this way it won’t make a mess when you turn the mixer on). Turn the mixer on and slowly pour in the kefir, let it beat until fully combined, scraping the bottom to ensure the batter is all incorporated.
Add the sakura sprinkles and fold them in with a rubber spatula. Pour the batter into the bundt pan and bake for about 45 minutes until you can press the center ring of the cake and it springs back. Allow to cool in the pan for about 5-10 minutes then turn it upside down onto a plate. Let it cool fully.
Make the glaze by combining all the ingredients into a paste. To make a thick glaze add less juice, to make a thin add more. Pour it over the cooled bundt. Add remaining sprinkles on top.
Kept in an airtight container at room temperature, the cake stays moist for 3 days.