Makes about 4 dozen 3-inch cookies
In a small bowl, rub zest and sugars together with your fingertips until the mixture is moist and aromatic.
In the bowl of a standing mixer fitted with the paddle attachment, blend zest, sugars, and butter until the mixture becomes smooth and creamy. Add egg yolks one at a time, mixing until each addition is fully incorporated. Add vanilla extract and mix until just blended.
Add flour, cardamom, and salt and blend on low just until dough begins to come together. (The dough should be worked as little as possible.)
Scrape dough onto a lightly floured work surface and, if necessary, gently knead it so it comes together. Divide dough in half and wrap each half in plastic wrap and refrigerate for at least 2 hours. (The dough may be kept in the refrigerator for up to 3 days, or made ahead and frozen for up to 1 month.)
Preheat oven to 350 degrees.
Remove one portion of dough from refrigerator and place on a well-floured surface so dough will not stick -- alternatively, you can roll the dough between 2 sheets of plastic. Roll out dough to 1/4-inch thickness and, using a 3-inch cat-shaped cookie cutter, cut out cookies. Place cookies on a baking sheet lined with parchment paper and refrigerate for 30 minutes. Meanwhile, repeat this process with remaining portion dough. Gather any scraps, wrap them in plastic, and refrigerate at least 15 minutes before rerolling.
Bake cookies one sheet at a time for 13 to 15 minutes or until they are a light golden brown. Transfer cookies to a wire rack to cool completely and repeat with remaining cookies. Once cookies are completely cool, use an offset spatula to spread ganache on cookies; decorate as desired.