• Zest the lemon into the sugar and massage with a gloved hand to distribute. In a medium bowl combine the flour, baking powder and cardamom.
• Cream the butter and sugar on medium speed until light and fluffy. If your butter is room temperature, this takes 1-2 minutes max.
• Add the egg and beat until fluffy. Add rum and beat to combine.
• Sift the dry ingredients directly into the bowl. Mix on low until just combined.
• Fold in the sliced almonds and candied lemon peel. I do this in the mixer on low—just don't overmix.
• Shape into two 2-inch logs using parchment paper. Wrap in plastic wrap and chill until firm—several hours or overnight.
• Preheat the oven to 350°F (176°C). Cut ¼-inch slices and place on parchment-lined baking sheets.
• Bake for 7-8 minutes. They will look matte and will have puffed slightly.
• Cool for 2 minutes on the baking sheet, then move to a wire rack to cool completely.

To Make the Rum Glaze:

• Whisk together rum and powdered sugar until smooth.
• Transfer to a disposable piping bag or zip-top baggie. Cut a small hole. Drizzle glaze over cooled cookies. To flood them, draw a circle with glaze about ¼ inch inside the edge, then squeeze to fill the circle. Let dry before stacking.