Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit).
In a mixing bowl, combine the chilled butter and flour. Using your fingertips or a pastry cutter, work the mixture until it resembles a wet sand-like texture.
Add the condensed milk to the mixture and stir until a soft dough. Be careful not to overmix. If you find the dough to be too sticky consider adding 1 tbsp flour to form a soft dough.
Scoop out approximately 1 tablespoon of dough and roll it into a ball. Place the dough balls onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.
Using your thumb or the back of a spoon, make an indentation in the center of each dough ball.
First Way: Fill each indentation with approximately 1/2 teaspoon of lemon curd. Be careful not to overfill.
Bake the cookies in the preheated oven for 8 to 12 minutes, or until the edges are lightly golden.
Remove the cookies from the oven and allow them to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
Once cooled, serve and enjoy these delightful 4-ingredient lemon curd cookies!
Second way: Follow the steps until making an indentation on the cookies. Instead of filling it before baking, bake the cookies as per baking instructions
If you feel cookies have puffed up, press it down one more time and then fill the cookies with lemon curd.
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Notes
Chill the butter: To achieve the desired sandy texture, make sure your butter is well chilled before combining it with the flour. Cold butter helps create a flaky and tender cookie.
Make uniform indentations: When scooping out tablespoon-sized portions of dough, use the back of a spoon to make a well in the center of each cookie. Make sure the indentations are evenly sized and deep enough to hold the lemon curd. This will ensure consistent results and prevent the curd from overflowing during baking.
Fill the indentations carefully: When adding the lemon curd to the cookies, use a small spoon or a piping bag for more precision. Fill each indentation with about 1/2 teaspoon of lemon curd, making sure not to overfill. Excess curd may spill out while baking and affect the cookies' appearance and texture.
Avoid overcrowding the baking sheet: Give the cookies enough space while baking. Place them about 2 inches apart on the cookie sheet to ensure even air circulation and prevent them from merging together.
Cool the cookies completely: Once the cookies are baked, allow them to cool on the baking sheet for a few minutes before transferring them to a wire rack. This will help them firm up and prevent them from breaking.
Variation: You can add little lemon zest to the dough to amp up the lemon flavor quotient. I have a great hack to zest lemon the proper way. Feel free to check it out. Or try experimenting with other flavours like vanilla extract or fill it with lemon custard instead.
Storage: Cookies filled before baking can be stacked, stored and transported. If you choose to fill the cookies after baking then the cookies has to be stored in a single layer only.