½ cup (120 grams) fresh lemon juice (from 3 to 4 lemons)
2 large eggs (100 grams)
2 large egg yolks (37 grams)
1 tablespoon (2 grams) finely grated lemon zest
¼ cup (57 grams) cold unsalted butter, cubed
Instructions
Place a fine-mesh sieve over a medium bowl, and set aside.
In a separate medium bowl, whisk together the sugar, cornstarch, and salt. Gradually add the lemon juice, and whisk until the cornstarch dissolves completely. Add eggs and egg yolks, and whisk until well blended.
Set the bowl over a saucepan of simmering water, making sure the bottom of the bowl does not touch the water. Cook the mixture, whisking constantly, until it begins to thicken, 3 to 4 minutes. Then whisk vigorously for 1 minute more. It should have a pudding-like consistency. Remove the bowl from the pot of simmering water.
Press the curd through the sieve. Whisk in the lemon zest and the butter, 1 to 2 pieces at a time, letting the cubes melt before adding additional butter. Let the curd cool to room temperature.
Once cool, press a piece of plastic wrap directly against the surface of the lemon curd to prevent a skin from forming, and refrigerate until well chilled and set, at least 6 hours.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/lavender-sandwich-cookies-lemon-curd-filling/