1. Preheat oven to 350°F. In a large bowl, beat butter and sugar with an electric mixer on medium speed until creamy. Add egg, lemon extract, and lemon zest and beat until well blended.
2. Add flour, baking powder, and salt to sugar mixture alternately with milk until well blended. Stir in blueberries. Drop by teaspoonfuls 2 inches apart onto greased cookie sheets.
3. Bake 12 to 15 minutes. Let cookies cool on sheers 2 minutes, then remove to a rack and let cool completely.