Preheat oven to 325 degrees F. In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add the 1-1/2 cups granulated sugar, the baking soda, cream of tartar, and salt. Beat until well mixed. Add oil, egg, vanilla, and lemon extract. Beat until well mixed. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour and the lemon peel.

Shape dough into 3/4-inch balls. Place balls 2 inches apart on an ungreased cookie sheet. Dip the bottom of a glass in additional granulated sugar and slightly flatten each cookie.

Bake in preheated oven about 10 minutes or just until edges start to brown. Transfer to a wire rack; let cool.

Spread about 1/2 teaspoon of the lemon curd on the bottom of each of half of the cookies. Top with remaining cookies, flat sides down, pressing lightly together. If desired, sprinkle tops of assembled sandwich cookies with powdered sugar and colored sugar. Makes about 60 sandwich cookies.

To Store: Layer unfilled cookies between waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months. To serve, thaw cookies if frozen. Assemble as directed in step 4.