Preheat oven to 350°F.

Whisk together flour, cocoa, baking soda, and salt in a bowl and set aside.

Stir together buttermilk and vanilla in a small bowl and set aside as well.

Beat together butter and brown sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy, (about 3-5 minutes) then add egg, beating until well combined.

Reduce speed to low and alternately mix in flour mixture and buttermilk in batches, beginning and ending with flour, scraping down side of bowl occasionally, and mixing until smooth.

Spoon small mounds of batter about 2 inches apart onto 2 parchment lined baking sheets. Bake in upper and lower thirds of oven, switching position of sheets halfway through baking, until tops are puffed and cakes spring back when touched, 11 to 13 minutes.

Transfer with a metal spatula to a rack to cool completely.

To assemble the pies, spread a rounded tablespoon of frosting (see recipe above) on to the flat sides of half the cakes.

On the other half of the cakes, spread a teaspoon of your favorite raspberry jam.

Use an off-set spatula to spread the jam all the way to the edges of the cakes.

Gently press a frosting filled side and a jam filled side together to create your Whoopie Pies.

To freeze the whoopee pies, wrap them individually in plastic wrap and freeze in a single layer until firm. Pies will keep well wrapped in the freezer for up to six weeks.