Combine egg yolks with 1 Tbsp sugar in mixer with whisk attachment. Mix until yolks lighten in color and begin to form ribbons. Slowly add coconut oil, then matcha colada, then matcha powder. In separate bowl, whisk together flour and cornstarch. Add flour mixture into matcha mixture a few spoonfuls at a time until well combined. Reserve.
In separate mixing bowl, combine egg whites with sugar in mixer with whisk attachment. Whip egg whites until they reach a soft peak. Combine 1 Tbsp egg white mixture to matcha mixture and stir to combine thoroughly. Add egg white mixture to matcha mixture, ⅓ at a time, folding gently to combine.
Preheat oven to 325F. Spray three 4” springform molds or one 9” springform mold with nonstick spray. Dust inside of mold with extra flour and shake off excess. Pour cake batter into mold, filling approximately halfway. Place cakes into middle rack of oven and bake, approximately 25-35 minutes for 4” cakes and 55-65 minutes for 9” cake or until a toothpick inserted at center can be removed cleanly. Let cool.
Place butter in mixing bowl in mixer with paddle attachment. Whip butter until soft and creamy. Add sugar and continue to cream until soft and smooth. Drizzle in white chocolate and matcha powder, mix until thoroughly combined. Use to frost cake if desired.