In a medium-sized bowl, cream the butter, sugar, and instant coffee until light and fluffy.
Mix in the egg.
Mix in the vanilla extract, salt, and flour until fully combined.
Divide the dough in half and press each half into a flat disc. Wrap in plastic wrap and refrigerate for four hours or overnight.
Preheat oven to 350 F.
Roll out the cold dough on a lightly floured counter or silicone mat to about 1/8" thick (no need to break out your ruler) and cut with cookie cutters or the rim of a glass. I used 2 1/2" fluted cookie cutters in calculating the yield.
Transfer cut cookies to cookie sheets and bake for 10 minutes or until the edges just start to brown. (Sometimes it can be tough to transfer the cut out cookie dough to the cookie sheet. To help with this, roll the dough out on a silicone mat and place the whole mat with the cut out cookies into the freezer for just a few minutes before transferring it.)
Immediately transfer to a cooling rack to cool.
If you roll the dough thicker (1/4" instead of 1/8"), the cookies will still be crispy on the outside but their insides will be softer.If you prefer, you can use espresso powder instead of instant coffee. Cut the amount in half, so use 1 tablespoon instead of 2 tablespoons.Store the cooled cookies in container that is not airtight. This could be a bakery-style box or a paper bag. I use a plastic container with the lid slightly propped open.The cookies will last up to one week at room temperature. They also freeze really well in an airtight container - just defrost and enjoy!