Place the freeze dried strawberries in the bowl of a food processor and process for 60 seconds until you have a fine powder.
In the bowl of a stand mixer fitted with a paddle attachment, or in a large bowl using a hand mixer, cream the butter for 30 seconds at medium speed. Add the powdered sugar, salt, and vanilla extract, and mix to combine.
Sift the strawberry powder and flour into the butter mixture. This will ensure that any larger bits of freeze-dried strawberries or pieces of strawberry seeds get removed. Mix on low until dry ingredients are well incorporated and a soft dough forms.
Tear off a sheet of plastic wrap and use a rubber spatula to scoop the cookie dough out of the bowl onto the plastic wrap. Shape it into a round or square log (a pastry scraper is particularly useful for getting sharp corners on a square log). Refrigerate for at least an hour or up to 24 hours.
When you are ready to bake, remove shortbread dough from fridge and let sit on the counter to warm up for 10 minutes. This will make it much easier to slice.
Preheat oven to 350 F and line a baking sheet with a piece of parchment paper or a silicone baking mat. Pour some coarse sugar or pink sanding sugar into a shallow bowl.
Using a sharp knife, cut dough into 1/4-inch thick rounds. Press the sides of the cookie into the sanding sugar to get the sugar to adhere.
Place cookies on cookie sheet, and bake in preheated oven for 20 minutes until the cookies are set, pale pink, and the edges of the cookies are slightly golden brown. The baked cookie will continue to set as it cools.
Let cool for 5 minutes on baking sheet, then transfer to a wire rack.
Cookies will keep in an airtight container for several days.