Place softened butter into a mixing bowl and mix with a kitchen aid mixer or hand mixer until it is creamy, about 2 minutes.
Add powdered sugar, vanilla extract, and salt to the butter and mix until well combined.
Add one egg white and mix until blended.
Take the mixing bowl out of the kitchen aid mixer and add the flour. Use a wooden spoon or your hands to incorporate it. Don't work the dough for too long, or you will end up with a rubbery mixture. Mix just long enough until you don't see any more flour.
Take the dough out of the bowl, put it on a plastic wrap, and wrap it up. Place it in the refrigerator for at least 4 hours - preferably overnight.
Forming
Line a baking sheet with parchment paper.
Cut the dough in half and take one half of the dough out of the fridge (it will be hard if you made it the day before), and work it with your hands for about a minute. It should still be firm but workable once done.
Roll it out with a rolling pin on a well-floured work surface until it's about 2-4 mm thick. Use light, consistent pressure, and turn your dough with your hands as you go so that it will be evenly rolled out. If the dough gets a little sticky, lightly dust it with flour.
Cut with a round cookie cutter 4-5 cm/2 inch big cookies (3 cm/1 inches for smaller Spitzbuben).
Place the cookies on the lined baking sheet.
Use a smaller cookie cutter to cut a "window" in half of the cookies. These will be the top of the cookies.
Repeat with the other half of the dough.
Preheat the oven to 392°F or 200C°.
Place the baking sheet in the fridge (or outside if it's cold enough) for about 20 minutes.
Bake for 7-10 minutes or until light golden brown. Baking time depends on how thick you rolled yours. Stay close to the oven and watch them. One minute too long in the oven, and you will have burnt cookies.
Remove cookies from the baking sheet and let them cool on a cooling rack.
Filling the cookies
Once cooled, flip all the cookies without "windows." Then, with a knife or a spoon, spread raspberry jam on the bottom side (the side that was on the baking sheet).
Dust the cookies with "windows" with powder sugar and place them on top of the cookies with the raspberry jam.
Notes
Spitzbuben stay good for 2 weeks in an airtight cookie tin.