Step 1Place a medium-mesh sieve over a large bowl or mixer bowl. Place the pink peppercorns in the sieve then use your hands to rub them against the mesh until almost all of their skins fall into the bowl below. Transfer the skinned peppercorns to a spice grinder and process until finely ground. Scoop out 1 teaspoon ground pink pepper and add it to the skins in the bowl; discard or save the rest of the ground pink pepper.
Step 2In the bowl with pink pepper, add the butter, sugar, vanilla and salt and beat on medium-low speed of a mixer until creamy, about 2 minutes (see Baker’s Note). Add the egg and beat until smooth. Add the flour and beat on low speed until just combined. Split the dough in half and place each half on a sheet of plastic wrap. Flatten each into a disk, wrap and refrigerate until firm, at least 1 hour.
Step 3Line 2 baking sheets with parchment paper. Place 1 dough disk on a lightly floured work surface and use a rolling pin to flatten until 3/16 inch thick. Using a 3 ¾-inch-long diamond cutter, cut out cookies, rerolling scraps as many times as necessary, and arrange 1 inch apart on the prepared baking sheets. Refrigerate the cookies on the baking sheets for 30 minutes.
Step 4Heat oven to 325 degrees.
Step 5Using a 1 ¼-inch-long diamond cutter, cut out shapes from half the cookies so the holes are slightly off-center. Place the small cutouts around the larger cookies on the same baking sheet or discard.
Step 6Bake, rotating the baking sheets front to back and top to bottom halfway through, until the cookies are set and dry to the touch (they will be barely colored on the bottom), 10 to 12 minutes. Let the cookies cool on the baking sheets for 1 minute, then transfer to a rack to cool completely. Repeat with the remaining dough to make more cookies.
Step 7Spoon 1 teaspoon jam onto each whole cookie, spreading it to within 1/4 inch of each edge. Cover each with a cookie that has a hole cutout. Melt the white chocolate, then drizzle it on the top of each cookie so the lines are parallel with the long center and slightly off-center opposite the cut hole. Let the white chocolate harden before serving.