For the cookies: Cream butter and sugar. Add eggs and vanilla- beat well. Add flour, baking powder, and salt, mix well. Cover and refrigerate until firm enough to roll- 45 minutes or so.
Divide the dough in half, and roll out to 1/4 inch thickness. Cut one batch of bottoms, then follow with an equal number of tops until you run out of dough, rolling the cut out centers back into the rest of the dough. (I used a large glass for my cookies, and a baby bottle cap to cut out the centers of the tops.).
Bake at 375 for 6-8 minutes 'til lightly browned. (I normally like chewy cookies, and under cook my dough- these are best if they aren't overly chewy for structural reasons.).
Cool cookies on a rack when they come out, placing the bottoms upside down once they are cool enough to handle. Sprinkle the tops with powdered sugar if desired.
Meanwhile, combine the berries, sugar, and jelly in a small saucepan over medium-high heat. Bring the mixture to a boil, reduce heat to low and simmer for 3-5 minutes. (I used my hand blender to smooth out the berries.) Remove from heat, allow to cool a little- the goal is to have it warm enough to spread on the cookies, but not too hot to handle.
OK, the assembly: spread a thin layer of filling onto the bottom cookie, keeping away from the very edge. Top off with a top, being careful not to disturb the powdered sugar.
After all of the cookies are 'glued' together, evenly distribute the remaining filling between the cookies, spooning it into the centers. Allow the centers to cool completely before moving (aprox. 30 minutes.) I placed a layer of wax paper in between when I stacked the cookies, because while the filling firms and isn't at all sticky, I didn't want to test it out.
EDIT: After making these with a tough batch of berries I discovered that you will need to add about 1/3 cup of flour to thicken the sauce if you strain the berries out - just bring it to a boil after straining.