1 (15.25 ounce) package lemon cake mix

1 small package vanilla instant pudding

4 eggs

3/4 cup water

3/4 cup vegetable oil

1 cup sour cream

2 Tablespoons lemon juice

1 cup (2 sticks) butter, softened to room temperature

1 teaspoon vanilla extract

1/4 teaspoon salt

1/2 cup seedless blackberry jam

4 cups powdered sugar

Blackberries, for garnish

Preheat oven to 350 degrees F.  
Line cupcake tins with 24 paper liners.  
In a large mixing bowl, combine cake mix and pudding.  
Add eggs and beat until smooth.  
Add water, oil, sour cream and lemon juice and mix until combined.  
Fill cupcake tins 2/3 of the way full with batter.  
Bake for 15-20 minutes, or until an inserted toothpick comes out clean.  
Let the cupcakes cool completely.  
For the frosting,  beat all ingredients together until light and fluffy.  
Pipe onto cooled cupcakes and top with a fresh blackberry.