In a bowl cream together butter, powdered sugar, vanilla bean paste, and cardamom until light and fluffy. Around 2-3 minutes.
Add egg yolk and continue to mix until no trace of egg remains.
Add the flour, cornstarch, and salt and mix to combine on low speed or by hand with a spatula. Do not overmix.
Wrap the dough in plastic wrap and refrigerate for at least an hour. The dough will last 2 days in the fridge.
When ready to bake, remove the dough from the fridge for 20-30 minutes to soften slightly.
Preheat the oven to 350*F.
On a floured work surface and with a floured rolling pin, roll the dough out to a ¼ inch thickness.
Using a cookie cutter, I used a 4 inch Christmas tree shape, cut out shapes. *SEE notes*
Gently press the leftover dough together, being careful not to add too much flour and continue to cut out shapes until all the dough is cut.
Using a spatula, transfer the cut out cookies to a parchment lined baking sheet.
Bake for 9-10 minutes or until the outer edges of the cookies are barely golden.
Let the cookies cool on the baking sheet for 10 minutes before transferring to a wire rack to continue to cool.