Beat butter with sugar until light and fluffy; beat in lemon rind. Beat in yolks, then lemon juice. Stir in flour and poppy seeds until fully incorporated. Divide dough in half and flatten into discs; refrigerate until well chilled, at least 1-1/2 hours.

Glaze: With fork, whisk together icing sugar, lemon rind and juice until smooth; keep at room temperature.

One at a time, on lightly floured surface or between two sheets of waxed or parchment paper, roll out each disc to scant 1/4-inch/5 mm thickness. With 2-inch/5 cm heart-shaped cookie cutters, and refrigerating and rerolling scraps, cut out cookies; place, about 1 inch/ 2.5 cm apart, on parchment paper–lined rimless baking sheets.

Bake in 300F/150C convection or conventional oven until bottoms and edges are golden, 13 to 14 minutes or 20 to 21 minutes, respectively. While still warm, spread each cookie with about 1/4 tsp/1 mL glaze and transfer to rack; let cool. (Make-ahead: Store in airtight container for up to 5 days.)

Makes about 52 cookies.