Preheat the oven to 350 degrees F. Line a 12 cup muffin tin with paper liners.
Using an electric mixer, beat butter, powdered sugar and lemon zest in a large bowl until fluffy and well blended. Add eggs; beating to blend. Beat in half the flour, then buttermilk and lemon juice, then the remaining flour.
Drop a spoonful of the cupcake batter into the bottom of each muffin cup. Spoon 1 teaspoon of raspberry jam on top of the batter of each muffin cup. Divide remaining batter among muffin cups to top the jam.
Bake for 18 to 22 minutes, until toothpick inserted into the center of a cupcake comes out clean. Cool cupcakes completely before frosting.
FROSTING
In a large mixing bowl, beat butter and raspberry jam together until well mixed and smooth. Add powdered sugar, a cup at a time, until you reach a consistency that you desire. I used 3 cups for this recipe, which I found perfect for piping.
Frost cupcakes either by spreading frosting onto the cupcakes with a knife or by scooping the frosting into a piping bag for a more decorative look.