Prepare and roll out cookie dough. Cut using cutter. Bake and cool cookies.
Use tip 2 and outline bottom edge and sides of cookie in full-strength rose royal icing and outline envelope flap in full-strength white royal icing.
Fill in with thinned white royal icing. Immediately sprinkle with pink sugar. Fill in with thinned rose royal icing. Let dry.
Use tip 2 and full-strength royal icing to overpipe outlines in corresponding icing colors. Use tip 5 and full-strength red royal icing to pipe heart. Pat smooth with finger dipped in cornstarch. Let dry.