Put the egg white in a bowl and beat, gradually adding honey, until stiff peaks form and you have meringue.
Combine softened butter and powdered sugar in another bowl and mix until soft.
Gradually add the meringue from Step 1 to the butter mixture from Step 2 and mix on low speed.
Add rum to the mixture from Step 3. Mix on high speed until creamy.
Finally, add vanilla beans and it's done. Chill in the refrigerator.
Make sandwich cookies or macarons...
If you're making rum raisin butter sandwich cookies, add a little extra rum (about 1 teaspoon).
Story Behind this Recipe
This is the buttercream my family likes for spreading on cookies or bread. I used it as macaron filling and gave it as a gift and the receiver loved it!
Adding honey to the egg white makes the cream turn out really thick (You can use granulated sugar or powdered sugar instead, but the cream will be thinner). Beat the egg white well. If you use 30 g of powdered sugar, the buttercream will be very sweet, so adjust the amount to your liking.