In a mixing bowl, cream butter and sugar together, then add egg and beat in well.
Add lemon juice and zest and mix until well blended.
In a separate bowl, whisk salt, baking powder and flour until combined. Then add to wet ingredients, mixing until blended. Be careful not to overmix, or cookies will turn out less tender.
Roll cookies out and cut into desired shapes. Place on parchment lined, ungreased cookie sheet.
Bake at 350 degrees for 8-10 minutes or until edges appear lightly golden.
Combine glaze ingredients and whisk until smooth. Allow cookies to cool slightly before glazing. Drizzle on glaze and sprinkle with pistachios. Let cool completely before eating.
You may want to place cookies on a wire rack to glaze. This will allow you to completely cover the top with glaze. Use a cookie sheet under the rack to catch drips. Allow glaze to set before removing cookies from rack.