Start by making homemade lemon curd. It's not hard but you do have to make it ahead of time so that it has time to chill. 

Preheat your oven to 350 degrees F.

In a stand mixer or with an electric mixer, beat the butter until light and fluffy.

Add the vegetable oil, white sugar, powdered sugar, vanilla, and egg, and beat until fluffy, scraping the sides and bottom of the bowl.

Add the flour to the bowl, but don't mix it in. Make a well in the center of the flour and add the baking soda, cream of tarter, and salt. Stir it in with a small spoon, then beat the flour mixture in until just combined. The dough is on the drier side.

Using your hands or a cookie scoop, form the dough into balls a little larger than 1 tablespoon. Line them up on a cookie sheet lined with parchment paper or a silpat. (you don't need to grease it).

In a shallow bowl, add 1/4 cup sugar. Get your fingers wet and rub them on the bottom of a glass. Dip the glass into the sugar, then smash each cookie. Dip in sugar and make sure the glass is coated with sugar for every cookie. You want them to be flat, but not so flat that they bake crispy. I like the dough to be a tiny bit less than half an inch thick. See photos.

Bake in the preheated oven for 6-8 minutes. Take them out when they are not quite brown on the edges, and still a little shiny on top (just a liiiittle bit).

Let cool for a few minutes, then transfer to a wire rack and cool completely.

Once the cookies are completely cool and the lemon curd is thoroughly chilled, spread some lemon curd on the top of one cookie, then top with another cookie. Or if you prefer, you can just spread the lemon curd on top of each cookie. These are really good with strawberries on top, too!