I originally found this recipe in Gourmet magazine, and made them at Christmastime. One year I had uneaten cookies from several varieties that I had made. I told my children I felt bad about it after all the work. They told me, "Really, all you should make is the Spitzbuben!" Good idea. The smarty pants tip is that the original recipe had the dough being chilled in a disk, and rolled out to 1/4" and cut with a 1 1/2" round cutter. I figured it would be much easier to shape it into a 1 1/2" log and cut it into 1/4" slices using a wire cheese slicer. Another change that I made was the original recipe called for 2 tsp powdered egg whites mixed with 2 tbsp warm water. This is the equivalent of 1 egg white, so whichever you have on hand is fine. I have made these using both jams, but the raspberry is definitely favored. —Marji
Sift the flour, confectioner's sugar, vanilla powder and salt together.
Beat butter in mixer until creamy. Mix in the flour mixture at low speed just until blended. Form the dough into a 1 1/2" log. It's a pretty firm dough, so it is easy, but you could use a paper towel cardboard roll cut down one side to help shape your plastic wrap covered log. Chill under firm, about 2-3 hours.
Preheat oven to 300*, and line baking sheet pans with parchment paper.
Slice the log into 1/4" rounds using a wire cheese slicer (I like using a marble cheese slicer board). Place 1" apart on the parchment. Brush cookies with egg whites and sprinkle with sanding sugar.
Bake until pale golden, about 10-15 minutes depending on your oven, then transfer to a rack to cool. Once cool, place about a half teaspoon of jam on half of the cookies, and then top with the other half, pressing gently to spread the jam.