01 -
In a large mixing bowl, beat the butter and sugar with an electric mixer until well combined. Add the eggs and yolks and beat for 1 minute. Add the lemon juice and mix until blended - the mixture will look lumpy.
02 -
Transfer the mixture to a medium, heavy-based saucepan and cook over low heat until it melts. Increase the heat to medium and cook, stirring constantly, until the mixture thickens. It should leave a path on the back of a spoon and register 170°F on a thermometer. Don't let the mixture boil. Once completely melted, it will thicken quickly, so watch it closely.
03 -
Remove the curd from the heat and stir in the lemon zest. Transfer to a bowl. Press plastic wrap directly on the surface of the lemon curd to prevent a skin from forming and chill in the refrigerator. The curd will thicken further as it cools.
04 -
Preheat oven to 350°F. Grease a mini muffin tin or line with mini cupcake liners.
05 -
In a small bowl, combine the all-purpose flour, whole wheat flour, salt, baking soda, and cream of tartar; set aside.
06 -
In a large bowl, cream butter and both sugars until light and fluffy. Beat in the oil, egg, lemon extract, and vanilla extract. Add the flour mixture to the creamed mixture and stir until combined.
07 -
Drop one tablespoon of dough (a #50 cookie scoop works well) into each cup of the prepared mini muffin tin. Bake for 8 minutes.
08 -
Remove from oven and immediately make an indentation in the center of each cookie using the end of a wooden spoon handle. Fill each indentation with a teaspoon of prepared lemon curd.
09 -
Return to the oven and bake for an additional 4 minutes, or until cookies are firm and lightly browned on the sides. Remove to wire racks to cool.
10 -
Once cooled, sprinkle the edges of the cookies with powdered sugar if desired. Store in an airtight container.