Preheat oven to 400°F. Line baking sheets with parchment or silicone baking mats.

In the bowl of a stand mixer fitted with the paddle attachment, cream butter on medium until smooth and glossy. Slowly add sugar and cream until light and fluffy, about 5 minutes.

Add egg whites in 3 additions, beating on medium until completely incorporated before adding the next bit.

Turn off mixer, add about a third of the flour, then beat on low until just incorporated. Repeat adding thirds of the flour, twice more.

Add vanilla and mix on low until incorporated.

Transfer batter to a piping bag fitted with a 1/4-inch round tip.

Pipe out 2-inch long strips onto baking sheets, leaving an inch of space in between.

Bake 11-12 minutes, or until lightly golden. Remove from sheets and cool completely on racks.

If desired, melt chocolate in a double boiler set over -- not in -- simmering water. Then spread jam on the bottom of a cookie, press another cookie onto the jam, and dip in chocolate. Set on lined baking sheets, and refrigerate until chocolate is hardened.