In bowl, whisk 4 cups/1 L of the flour with the baking powder; set aside.

In heavy-bottomed saucepan over medium heat, stir together sugar, honey, cinnamon, nutmeg and cloves; bring to boil, stirring constantly. Stir in almonds, hazelnuts, orange and citron peels and lemon rind; reduce heat to low and cook, stirring constantly, for 10 minutes. Add flour mixture, 1/3 cup/75 mL at a time, stirring after each addition until fully blended; stir in kirsch and remove from heat.

Sprinkle work surface with remaining flour; set hot dough on top and, wearing rubber gloves if necessary, knead until smooth. Divide dough in half, flatten into discs, then shape into squares.

Cut parchment paper to fit each of two rimless baking sheets. On each sheet of paper, roll still-warm disc into 1/4-inch/5 mm thick rectangle; leaving on paper, transfer to baking sheet and prick with fork. Let rest overnight (uncovered) in cool, dry place.

One pan at a time, bake in centre of 425F/220C oven until top is lightly browned, 15 to 20 minutes.

Glaze: Meanwhile, stir icing sugar with kirsch until smooth and spreadable glaze, adding more kirsch if necessary just until easily spreadable.

Spread glaze over baked, still-hot cookie rectangles; let cool on racks until just cool enough to handle. Transfer to cutting board.

Trim off crispy edges (save for cook's treat); cut into 1-1/2-inch/4 cm squares and return to pans on racks; let cool completely. Let stand in airtight container for at least 24 hours before serving or eating. (Make-ahead: Store in airtight container for up to 8 weeks.)

Makes about 85 cookies.