Instructions

1. Preheat the oven to 350ºF. 
2. Line 2 8×8-inch baking dishes with foil, then lightly spray with nonstick cooking spray. Set aside.
3. Place the butter in the bowl of a stand mixer (or a large bowl is making by hand). Cream the butter until it is smooth, then add the sugar, baking soda, cream of tartar, and salt. Beat until combined. Beat in the egg and the vanilla, scraping the bowl as needed. Start adding the flour 1/2 cup at a time and mix until fully combined.
4. Press half of the dough mixture into each of the prepared baking dishes. Press into an even layer. Bake I the preheated oven until the bars are just set, about 12-13 minutes. Remove from the oven, let them sit in the pan for 5 minutes, then lift the foil out and place on a cooling rack to cool completely.
5. Slightly soften the ice cream and place in a large bowl. Add the lemon curd and stir to combine.
6. Take one of the baking dishes that you used for the bars and line with plastic wrap, letting the excess hang over the edges. Place one of the cookie bars in the pan. Spread the ice cream evenly over the cookie bar, then set the second cookie bar on top. Wrap with plastic wrap and place in the freezer to freeze overnight.
7. When ready to serve, remove the bars from the pan using the plastic wrap. Remove the plastic wrap and cut into 16 squares with a sharp knife. Serve immediately, or place back in the freezer until ready to serve.