Cream the butter and sugar together in the bowl of a mixer at medium speed until light and fluffy, around 5 minutes. Beat in the eggs, one at a time, until fully incorporated. Add the yogurt, vanilla, orange juice and orange zest, and mix until combined.
In a medium bowl, whisk together the dry ingredients, then add it to the wet mix in batches, stirring until just combined. Line a muffin tin with paper cups, then fill each cup ⅔ full with batter. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Cool completely.
For the Buttercream
In a large mixing bowl, beat together the butter, light corn syrup, vanilla, and kosher salt until light and fluffy, around 5 minutes. Slowly beat in the powdered sugar in batches, adding the heavy cream as necessary to thin the buttercream. Once the desired consistency is reached, beat in food coloring if wanted, or use as is.