Pre-heat oven to 350 degrees and line a cupcake tin with 12 papers.
In the bowl of a stand mixer or in a large bowl with a hand mixer, cream together butter, confectioners' sugar, and lemon zest on medium-high speed until light and fluffy, about 3 minutes.
Add eggs in one at a time, mixing well after each addition. Mix in vanilla extract.
In a separate medium bowl, whisk together flour, baking powder, and salt.
With mixer on low speed, beat in half the dry ingredients. Add buttermilk and lemon juice, mixing to just combine. Blend in the rest of the flour until just incorporated, taking care not to over-mix.
Fill cupcake papers a little more than ½ way with batter. Place 1 tsp of jam over each and use remaining batter to cover jam (it's OK if some jam is still peeking through).
Bake cupcakes for 19-22 minutes, until they're just turning golden at edges and a tester inserted in the middle comes out clean. Let cupcakes rest in tin for a couple minutes before moving to wire racks to cool completely.
Place pastry bag fitted with tip (I used 1M) in a tall drinking glass. Using a spatula, fill one side of the pastry bag with lemon buttercream. Fill other side with raspberry buttercream. Frost cupcakes using swirl design.
Top cupcakes with a fresh raspberry, tiny lemon wedge, and little straw.