Prepare lemon curd.

Preheat oven to 350° F.

Combine the flours, salt, baking soda and cream of tartar in a small bowl and set aside.

In a large bowl, cream butter and sugars until light and fluffy. Beat in the oil, egg and extracts. Add flour mixture to creamed mixture and stir until combined.

Drop one tablespoon dough into each cup of a greased mini muffin tin or lined with mini cupcake liners. Bake for 8 minutes.

Remove from oven and using the end of a wooden spoon handle, make an indentation in the center of each cookie. Fill with a teaspoon of lemon curd.

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.

Sprinkle the edges of the cookies with powdered sugar.

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 min. Add the lemon juice and mix until blended - the mixture will look lumpy.

In a medium, heavy-based saucepan, cook the mixture 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 will read 170°F on a thermometer. Don't let the mixture boil.

Remove the curd from the heat; stir in the lemon zest. Transfer the curd to a bowl. Press plastic wrap on the surface of the lemon curd to keep a skin from forming and chill the curd in the refrigerator. The curd will thicken further as it cools. Covered tightly, it will keep in the refrigerator for a week and in the freezer for 2 months.