In a small bowl, stir together flour, baking soda, and baking powder. Set aside.
In a large bowl, cream together butter and sugar until smooth. Beat in the egg and vanilla. Gradually blend in dry ingredients. Add enough of the buttermilk to moisten the dough and make it soft, not wet.
Roll rounded teaspoons of dough into balls and place on an ungreased cookie sheet. With a brush or fingers, moisten the top of each cookie with the remaining buttermilk and slightly flatten the top of each cookie.
Bake for 8 to 10 minutes or until slightly golden. Let stand for 2 minutes before removing to cool on a rack.
In a separate bowl mix sliced strawberries and sugar crystals and then top each cookie with desired amount of berries.
Add ½ cup + 2 tablespoons strawberry puree to a small saucepan.
Heat mixture over medium-low heat, and simmer, stirring occasionally until reduced by about 2/3 to 3 tablespoons, about 10 - 14 minutes (measure and if it isn't quite 3 tablespoons then return and continue to simmer, if it's not reduced to correct amount it will make frosting runny).
Pour reduced puree into a small bowl, and then freeze until cool (stir occasionally for even chilling, it will chill quickly in the freezer since it's such a small amount).
In the bowl of an electric stand mixer fitted with the paddle attachment, whip unsalted and salted butter until very pale and fluffy (nearly white.
Stop and scrape down bowl occasionally throughout entire mixing process if not using the paddle attachment that constantly scrapes bowl).
Mix in 1 cup powdered sugar, and then blend in 3 tablespoons reduced strawberry puree, vanilla extract, and optional red food coloring.
Add remaining 1 ½ cups powdered sugar and continue to mix until frosting is pale and fluffy, adding in an additional ¼ cup powdered sugar if needed to reach desired consistency.