Peruvian Dulce de Leche Alfajor Cookies

Ingredients

• 1 Can sweetened condensed milk - 14 oz (1 can), Used to make dulce de leche filling.
• 1.25 Cup all-purpose flour - 1 1/4 cups (150 g), 150 g equivalent given in source text.
• 1 Cup cornstarch - 1 cup (120 g), 120 g equivalent given in source text.
• 0.5 Teaspoon baking powder - 1/2 tsp (2 g), 2 g equivalent given in source text.
• 0.25 Teaspoon fine salt - 1/4 tsp (1.5 g), 1.5 g equivalent given in source text.
• 0.75 Cup unsalted butter, softened - 3/4 cup (170 g), 170 g equivalent given in source text.
• 0.75 Cup powdered sugar, divided - 3/4 cup (90 g), 90 g total; use 1/2 cup in the dough and the remaining 1/4 cup for dusting.
• 2 Each egg yolks - 2 large (36 g), 36 g total equivalent given in source text.
• 1 Each lemon - 1 (about 5 oz), Use 1 teaspoon finely grated lemon zest.

Instructions

1. Prepare the dulce de leche water bath

   1. Heat oven to *425°F*. Finely grate *1 teaspoon lemon zest* and set it aside; pour *sweetened condensed milk* into a 9-inch pie plate, cover tightly with foil, set the plate in a larger baking dish, and add hot water halfway up the plate.

2. Bake and cool the dulce de leche

   2. Bake the milk in the water bath for *75 to 90 minutes*, adding hot water if needed, until it is *thick and caramel-brown*. Carefully remove the foil, whisk the filling *until smooth*, cool completely, and lower the oven to *350°F*.

3. Mix the dry ingredients

   3. Line two rimmed baking sheets with *parchment paper*. In a medium bowl, whisk *all-purpose flour*, *cornstarch*, baking powder, and salt until evenly blended.

4. Cream the butter and sugar

   4. In a large bowl, beat *softened butter* and *1/2 cup powdered sugar* with an electric hand mixer until pale and creamy, about *2 minutes*. Beat in *egg yolks* and the lemon zest until smooth.

5. Make and chill the dough

   5. Add the dry ingredients to the butter mixture and mix on low speed just until *crumbly dough* forms. Gently press it together with your hands, divide in half, flatten into disks, cover, and chill for *20 minutes*.

6. Roll and cut the cookies

   6. Roll one disk at a time between two sheets of *parchment paper* to *1/4 inch thick*. Cut *2-inch rounds*, transfer to baking sheets 1 inch apart, and reroll scraps gently.

7. Bake the cookies

   7. Bake at *350°F* for *9 to 11 minutes*, until the tops look dry and the bottoms are *barely golden*. Cool on the pan for 5 minutes, then move to a wire rack to *cool completely*.

8. Fill and sandwich

   8. Spread *1 rounded teaspoon dulce de leche* on the flat side of half the cookies. Top with the remaining cookies and press gently until the filling reaches the edges in a *neat sandwich*.

9. Dust and rest

   9. Dust the filled cookies with *remaining 1/4 cup powdered sugar*. Let them rest for *20 minutes* so the cookies soften slightly before serving.