In a large mixing bowl, cream together the butter and confectioners’ sugar on medium-high speed until smooth, about 1-2 minutes. Beat in the egg and vanilla extract. Mix in the flour and salt on low speed until just incorporated.
Divide the dough into 3 separate chunks and color one red, one yellow, and one orange. Form each dough chunk into a ball and wrap tightly with plastic wrap. Refrigerate until chilled and firm, at least 2 hours.
When you are ready to bake the cookies, preheat the oven to 375˚ F. Line baking sheets with parchment paper and set aside.
Cut each dough disk in half. Work with half the dough at a time, re-wrap what you're not using and return it to the refrigerator.
Flour your work surface. Break the dough into small chunks and arrange randomly on your work surface. Squish the dough together to form one disk.
Roll the dough out to about ¼-inch thickness. Cut with a leaf cookie cutter and transfer to the prepared baking sheets.
Using the blunt edge of a butter knife, gently mark the veins of the leaf and sprinkle with orange decorating sugar (optional).
Bake 7-10 minutes (depending on the size of your cookies), rotating the sheets halfway through baking until fully cooked but not at all browned. Allow to cool on the baking sheet 5 minutes, then transfer to a wire rack to cool completely. *If you're using a large cookie cutter, you'll need to increase your baking time by a few minutes.
Repeat the process with the remaining cookie dough.
I used a 2 1/2 inch by 1-inch cookie cutter for my leaves and got about 14 cookies from this recipe. The number of cookies this recipe makes is all dependent on the size of your cookie cutter(s).