• Adjust oven rack to middle position and heat oven to 350 degrees.
• Grease a bundt pan liberally with olive oil cooking spray. Add powdered sugar to the pan and be sure to shake all the way around the pan. (Be especially sure that the inner cone of the bundt pan is coated in sugar so that the cake does not stick.) Set aside.
• In the bowl of the stand mixer, whisk together cake flour, baking powder, salt, baking soda, and 1 3/4 cups sugar until combined. Pour into a bowl and set aside.
• In clean bowl of a stand mixer fitted with whisk attachment, beat egg whites at medium-high speed until foamy, about 30-45 seconds.  With whisk still running, add in the remaining 1/4 cup sugar.  Continue to beat until stiff peaks just form, about 2 to 5 minutes(this will depend on humidity in your area as when the peaks will form). Transfer the whipped egg whites to a separate bowl and set aside.
• In bowl of the stand mixer, whisk together melted butter, buttermilk, rum, oil, vanilla, and yolks until combined. Using the whisk attachment again, slowly add the flour mixture to the bowl a little at a time. Mix until the ingredients are just incorporated. Stop the mixer and scrape whisk and sides of bowl. Return mixer for about 30 seconds.
• Remove bowl from stand mixer. Fold about 1/3 of the whipped egg whites into batter until just combined, then add the remaining whites and gently fold in until no streaks remain. Do not over fold and do not stir.
• Pour the batter evenly into the powdered bundt pan. Bake for 45 minutes or until a cake tester is inserted into the middle of the cake comes out clean. Remove from oven and let cool for 5 minutes. Poke holes with a tooth pick or small straw around the cake. Pour 3 tablespoons melted butter over the cake. Let sit for 5 more minutes.
• Take a butter knife and make sure to remove the cake from the sides of the pan. Place upside down on to a cooling rack. Let cool for 10 minutes. Serve immediately, or cover until ready to serve.

For Icing:

• In a bowl, mix in two mini bottles of Irish cream along with powdered sugar. Start with one cup of powdered sugar and add more as needed. Whisk until you have a thick but still runny consistency. 
• Pour over cake drizzling to cover both the inner and outer sides of the cake. Serve.