Preheat the oven to 375°F (190°C) and grease cookie sheets. In a bowl, sift together the flour, baking powder, and salt. In a large bowl, use an electric mixer to beat the sugar and butter until the mixture becomes lighter in color. Add the beaten eggs and lemon extract, mixing well. Alternately add the milk and the flour mixture in three parts, beginning with the milk. Carefully fold in the blueberries. Drop the batter by tablespoonfuls onto the prepared cookie sheets, spacing them about 1½ inches apart. Bake in the preheated oven for 12 to 15 minutes, or until the edges turn golden brown.