Preheat the oven to 350 degrees F, and line a cupcake pan with papers.
Place the flours, sugar, baking powder, baking soda, and salt in a large mixing bowl and whisk to combine.
Add the butter, and mix on medium-low speed, until the mixture resembles damp sand.
Stir in the peanut butter, then add the eggs one at a time, mixing until fully incorporated.
Scrape the bottom and sides of the bowl with a silicone spatula, then add the Greek yogurt, milk, and vanilla.
Mix on medium-high speed for approximately 90 seconds, to aerate the batter and build the cake's structure.
Place about 1/4 cup of batter in each well of the cupcake pan.
Bake for 14-16 minutes, or until a toothpick inserted in the thickest part of the cake comes out clean or with a few moist crumbs.
Cool completely, then cut a small well in each and fill with grape jam.
Top with buttercream and drizzle with more grape jam.