STIR flour with baking powder and salt in a medium bowl. Using an electric mixer on medium-high, beat butter with sugar in a large bowl for 2 min. Beat in egg, scraping down side of bowl as needed. Beat in vanilla, then reduce speed to low and gradually beat in flour mixture until just combined.
DIVIDE dough into 2 portions. Shape each into a ball, flattening slightly into a disc. Wrap separately with plastic wrap and refrigerate until firm, at least 1 hr or up to 1 week.
POSITION rack in centre of oven, then preheat to 350F. Line 2 baking sheets with parchment paper. Remove 1 disc from refrigerator and let sit for 5 min. Roll to 1/8 -in. thickness on a lightly floured surface. Cut out shapes with a 1 3/4-in. fluted square (or square) cookie cutter. Arrange on prepared baking sheets, 1/2 in. apart. Bake until cookies are golden, 9 to 11 min. Let cookies cool on sheets for 1 min, then transfer to a wire rack to cool completely. Repeat with remaining dough, chilling scraps as needed.
FLIP over parchment paper on baking sheets. Temper chocolate and cacao butter. Stir food colouring into chocolate until combined. Dip half of a cookie into chocolate diagonally. Shake off excess. Lay on prepared sheets. Sprinkle chocolate side of cookie with a pinch of peppercorns; repeat with remaining cookies. Let stand until chocolate is firm, about 30 min.
STIR jam with vinegar and remaining peppercorns. Spread half batch of cookies with about 1/2 tsp jam mixture, then sandwich with remaining cookies.
Chatelaine Cookies: Hamantaschen
Nutrition (per serving)
Kitchen Tip: Sandwiched cookies will start to soften after 2 days in a covered container. Store plain sugar cookies in a covered container up to 1 week, or freeze up to 1 month. Decorate with chocolate and sandwich with jam the night before serving for best results.