Preheat oven to 350. Line a baking sheet with parchment paper.
In a medium bowl whisk to combine flour, cocoa powder, baking powder, and salt.
In a separate medium bowl whisk to combine egg whites, Sweet N Low, butter, and vanilla.
Stir flour mixture into wet ingredients, then knead until mixture forms a dough. It will be very stiff.
Divide dough into 16 pieces, then roll each piece into a ball. Place on baking sheet and use thumb to press an indentation in center of each piece of dough.
Fill indentations in cookies with raspberry preserves.
Bake until cookies are firm, 8-10 minutes. Let cool completely on a rack on baking sheet.