Preheat oven to 350 degrees and spray a donut pan with non-stick cooking spray.
Combine the sugar, sour cream, sourdough discard, egg, egg yolk, coconut oil, butter & vanilla in a large mixing bowl. Use a hand or standing mixer to fully combine.
Transfer the batter into a piping or plastic bag and pipe the batter into each donut mold. Fill them about 3/4 of the way full.
Bake the donuts for 12-15 minutes or until lightly golden brown.
While the donuts are baking, make the glaze by combining all ingredients in a medium bowl and mixing with a hand mixer or whisk until fully combined.
Crush the Siete churro strips and place into a shallow bowl or plate.
Once donuts are baked, take out & let cool for about 5 minutes. Remove from mold, fold & coat each donut in glaze and then gently roll in churro strip crumbs.