Make the Lemon Curd:

• In a medium mixing bowl, cream the softened butter and sugar together with an electric mixer until smooth and light in color.
• Beat in the eggs and egg yolks one at a time until fully incorporated.
• Mix in the lemon juice. The mixture will look curdled—this is normal.
• Pour the mixture into a medium saucepan and cook over medium-low heat, stirring constantly with a wooden spoon or silicone spatula.
• Cook until the curd thickens and coats the back of the spoon—this takes about 10–15 minutes. Do not let it boil.
• Remove from heat and stir in the lemon zest.
• Transfer the lemon curd to a bowl and press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate until cooled and thickened (can be made in advance).

Make the Cookie Cups:

• Preheat oven to 350°F (175°C).
• Lightly grease a 24-cup mini muffin tin with nonstick spray or butter.
• In a medium bowl, whisk together the all-purpose flour, whole wheat flour, baking soda, cream of tartar, and salt. Set aside.
• In a large mixing bowl, cream the softened butter with the sugar and powdered sugar until fluffy.
• Add the oil, egg, lemon extract, and vanilla extract. Mix until fully incorporated.
• Gradually mix in the dry ingredients until a soft dough forms.
• Using a small cookie scoop, portion the dough evenly into the prepared mini muffin pan.
• Use a tart tamper or the back of a rounded teaspoon to gently press down the center of each ball of dough, forming a cup shape.
• Bake for 10–12 minutes, or until the edges are lightly golden but the centers are still soft.
• Remove from the oven and immediately use the back of a spoon to press down the centers again to reinforce the cup shape.
• Let the cookie cups cool in the pan for 5–10 minutes, then carefully remove them and transfer to a wire rack to cool completely.

Fill the Cookie Cups:

• Once completely cool, spoon about 1 teaspoon of lemon curd into the center of each cookie cup.
• Dust with powdered sugar before serving, if desired.