In a medium bowl, whisk together the flour, cornstarch, and salt until combined. Set aside.

In a large bowl using a handheld or a stand mixer fitted with a paddle attachment, beat the butter and 3/4 cup (150g) granulated sugar together on medium-high speed until creamed, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the lemon zest, lemon juice, egg, and vanilla bean paste and beat on high speed until combined, about 1 minute. The wet ingredients will look curdled, but will smooth out when you add the dry ingredients. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.

Add the dry ingredients to the wet ingredients and mix on low speed until combined. Dough will be very creamy. Cover and refrigerate for at least 3 hours, and up to 3 days. Chilling is imperative for this soft dough.

Line large baking sheets with parchment paper or silicone baking mats. Make room in the refrigerator for baking sheets, so the shape cookies can chill as the oven preheats in step 7.

Place granulated sugar in a small bowl. Scoop cold dough (about 1 Tablespoon (18g) of dough each) and roll into balls. Roll each dough ball in granulated sugar and place 2 inches apart on lined baking sheets.

Use your thumb to make an indentation in the center of each cookie dough ball. Fill each with 1/2 teaspoon of lemon curd.

. Place baking sheets with unbaked cookies in the refrigerator while the oven preheats. (Or transfer all cookies to 1 baking sheet, or a few plates, if your refrigerator doesn’t have room. I recommend chilling the shaped cookies for a few minutes, to prevent over-spreading.)

Once oven preheats, bake shaped cookies for 12–13 minutes, or until edges appear set and are very lightly beginning to brown. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.

In a small bowl, whisk together confectioners’ sugar and lemon juice. Drizzle over cooled cookies. (You can use a spoon or fork for this, or a squeeze bottle.) Icing will set at room temperature after about 30 minutes, and then you can stack, store, transport, and gift the cookies.

Cookies stay fresh covered at room temperature for up to 1 week.