2 1/4 cups unsifted all-purpose flour
1 teaspoon baking powder
1/2 teaspoon salt
3/4 cup (11/2 sticks) unsalted butter, slightly firm
1 tablespoon freshly grated lemon zest
3/4 teaspoon lemon oil
1 cup granulated sugar
2 large eggs
1 teaspoon pure vanilla extract
1. Make dough: Sift together flour, baking powder and salt. Set aside. In large bowl of an electric mixer on medium speed, mix butter, lemon zest, and lemon oil until smooth and creamy. Gradually add sugar, then eggs and vanilla extract, and beat until thoroughly blended, scraping down sides of bowl as needed. On low speed, add dry ingredients in two additions, mixing just until combined. Transfer dough to a smaller bowl, cover with plastic wrap and refrigerate dough for 1 hour.
2. Position shelves in upper and lower third of oven. Preheat oven to 350°F. Grease two cookie sheets. Using your hands, roll dough into walnut-sized balls, then place them on prepared cookie sheets, about 3" apart. Using a flat-bottom glass or a meat bâtarde covered with a damp paper towel or cloth napkin, flatten cookies to a 21/2" width. (Shift towel or napkin as needed if dough begins to stick.) Bake for 13-15 minutes, or until edges are lightly browned. Immediately after removing cookies from oven, loosen them with a thin metal spatula. When cool enough to handle, transfer to cooling racks.
3. Store in an airtight container, layered between strips of waxed paper, for up to 3 weeks. These cookies may be frozen.