Step 1

Combine the butter, sweetened condensed milk and salt in a large bowl. Using a spatula, mix everything until the butter is incorporated into the condensed milk. A few remaining lumps is okay!

Step 2

Slowly add the cornstarch, mixing with the spatula to combine. It will eventually get hard to use the spatula, and you can then use your hands. Mix just until a smooth dough forms. You might not need all the cornstarch and should avoid the temptation to add everything if it's not needed.

Step 3

Roll the cookie dough (about 1 teaspoon per cookie) into balls and press each ball with your thumb (like you would thumbprint cookies). Place the balls on a two baking sheets lined with parchment paper. Using a fork, slightly flatten the cookies, also making their characteristic fork indentations.

Step 4

Refrigerate the cookies for 30 minutes to avoid them spreading when baking.

Step 5

Preheat oven to 350ºF with a rack in the middle.

Step 6

Bake the cookies for 15 minutes or until they begin to gain some color on the bottom. They should still be quite pale on the top.

Step 7

Remove the cookies from the oven and let them cool slightly still on the baking sheets. After 15-20 minutes, carefully remove them to a wiring rack so they can finish cooling.