Preheat your oven to 350°F.
In a large bowl, cream together 1 cup butter and the ½ cup sugar for about 2-3 minutes until light in color and fluffy in texture.
Beat in the 1 egg & 1 tsp vanilla. Then use a wooden spoon to mix in the 2 ½ cups flour and 1 tsp baking powder.
The dough will look very dry and crumbly at first. Keep mixing until it sticks together in one ball. Your dough should be soft but not sticky. If your dough is very sticky, add a few more tbsp of flour (one at a time, testing between each) into the dough. I personally added about 3 tbsp of flour to my dough.
Once your dough has the right consistency, flour a countertop or large cutting board and use a rolling pin to roll out the dough to about ⅛” thick.
Use a 2.5” cookie cutter to cut out the top and bottom cookies from the dough. On the "tops", use another, smaller cookie cutter to cut out a center shape so that you can see the jam through the dough.
Line a baking tray with aluminum foil (shiny side up) and bake the cookies for about 8-10 minutes. I like mine to be just turning yellow on the bottom. Allow the cookies to cool on the tray, then remove the cookies from the tray.
Put ¼ cup powdered sugar in a sifter and sprinkle powdered sugar over the cookie tops.
Put ½ cup jam in a pot on the stove and heat until it just begins to boil. You can also microwave it for about 1 minute if that is easier.
Once the jam has begun to cool, spread an equal amount on each cookie "bottom". Place the "top" over the jam (being careful not to put your fingerprint in the powdered sugar), and allow the cookies to cool completely before enjoying.