In a large microwaveable bowl, add 1/2 cup butter. Heat in the microwave until it's melted.
Add 3/4 cup granulated sugar and use a whisk to combine.
Use a microplane grater to zest 2 lemons* into the bowl. You need about 1 tablespoon of zest.
Juice one of the lemons and measure out 1/4 cup lemon juice. You might be able to get this amount from 1 large lemon, or you might need 2 lemons.
Add 1/4 cup lemon juice to the butter and sugar mixture and whisk well.
Add 1 large egg to the bowl. (By this time, the melted butter should have cooled slightly. If it is still pretty hot, make sure you wait to add the egg so it doesn't curdle.) Whisk until smooth.
Add 1 and 1/2 cups all purpose flour that you have spooned and leveled. This means you should spoon the flour into the measuring cup and then level off the top. Don't stir in the flour yet!
On top of the flour in the bowl, add 1/4 teaspoon baking powder and 1/2 teaspoon kosher salt. Use your teaspoon to stir the baking powder and salt into the flour, making sure to get out any lumps.
Use a rubber spatula to combine the wet ingredients with the dry ingredients. Once all the flour streaks are gone and the mixture is well combined, stop stirring. Stirring cookie dough too much makes the cookies tough!
Cover the bowl with a lid or plastic wrap, and chill in the refrigerator for 45 minutes, or up to 2 days.**
When you are ready to bake, preheat the oven to 350 degrees F. Line 2 half baking sheets with silpats or parchment paper.
Sift 1 cup powdered sugar into a medium bowl.
Use a cookie scoop or a spoon to shape the dough into 1 and 1/2 inch cookie dough balls.
Roll the shaped cookies in the sifted powdered sugar.
Place the cookies on a baking sheet or a plate and place them in the fridge or freezer for 5 to 10 minutes.
Roll each cookie dough ball in sifted powdered sugar a second time. This is the step that will make sure your powdered sugar does not dissolve into the cookie while baking!
Line up the double-rolled cookie dough balls on a half sheet pan lined with parchment paper or a silpat. I usually put 12 on a pan.
Bake the cookies at 350 for 9-11 minutes, until the cookies are set on the edge when you tap the edge with your finger, but there is still a tiny bit of shine on top. The shine on top should be no larger than a quarter. If the cookies are completely matte on top, they will still be good, just not quite as soft. Underbaking these cookies is KEY to getting the fudgy texture we are after.
Immediately after you take them out of the oven (seriously, don’t wait) use two spoons to gently push each cookie together. I just used two regular spoons, the kind you eat cereal with. Push the cookie together so that it comes up a bit in the middle, that’s how you’re going to get a soft, thick center. If you wait even just a minute after taking them out of the oven, the brown edges will start to crisp up, and you won’t be able to shape the cookies. Work your spoons all the way around the edges so that your cookie is a nice circle shape. Work quickly to shape all the cookies before they crisp on the edges.
Sprinkle the hot cookies with lemon zest, if you want a little extra color!
Store cookies covered on the counter for up to 3 days.
Notes
*I like to use the zest from 2 lemons for this recipe. The zest is a powerhouse of flavor! You only need 1/4 cup lemon juice, which you can usually get from 1 large lemon. So if you want to just use 1 lemon for less waste, that's totally fine, your cookies just won't be QUITE as tart as if you used a full tablespoon of zest. **If you have chilled the dough and it has become quite hard, let it sit out at room temperature for 30 minutes before you try to scoop it.