Preheat the oven to 350°F. Line muffin pan with liners. I used two to keep the outside looking good.
Sift together the flour, baking powder, and salt into 1 bowl. Whisk together the yogurt, sugar, honey, eggs, grapefruit zest, and vanilla. Slowly incorporate the dry ingredients into the wet ingredients. With a rubber spatula, fold the vegetable oil and grapefruit juice into the batter, making sure it’s all incorporated. Pour the batter into the muffin tins and bake for about 20 minutes, or until a cake tester placed in the cupcakes comes out clean.
Meanwhile, mix the honey buttercream ingredients together.
When the cupcakes are done, allow them to cool in the pan for 10 minutes. Carefully place on a baking rack over a sheet pan.
For the frosting, combine the ingredients until thick and smooth. Place in a baggie, snip off the corner and pipe until each cupcake.