Step 1

In a large bowl, beat the butter and sugar together on medium-high speed for 1-2 minutes, until light and fluffy.

Step 2

Add the egg, lemon zest, and vanilla and mix until fully combined. Scrape down the sides and mix again for 10-20 seconds.

Step 3

Add the flour and salt and mix until just barely combined in a crumbly dough. Use your hands to press the dough together. If the dough is too dry, add water one tablespoon at a time to help it come together. Be careful not to add too much water, it should only be enough to bring the dough together, not enough to make it sticky. Form the dough into a disk and wrap it with plastic wrap. Chill for 2 hours. While the dough is chilling prepare the poppy seed filling.

Step 4

Once the dough is chilled, preheat the oven to 350°. On a lightly floured surface, roll the dough out to 1/8 inch thick. You may need to let the dough sit for a few minutes so it is a little easier to roll out without it cracking or crumbling. If it does crack or crumble, use your fingers to pinch the dough back together.

Step 5

Use a 3-inch round cooking cutter to cut out rounds of dough. Carefully transfer the rounds to parchment-lined baking sheets leaving 1 inch between them. Place 1 teaspoon of poppy seed filling or jam in the center of the dough. Fold up the side of the dough to form a triangle around the filling, pinching the corners together to prevent leaking while baking. You can rub a little water or beaten egg on the corners before pinching it together to help act as glue to keep it from opening. Gather the remaining dough and repeat, though the more the dough is rolled the tougher the cookies will be.

Step 6

Bake for 12-15 minutes, or until the cookies are just starting to turn golden brown around the corners. Let them cool on the baking sheet for 10 minutes before transferring to a cooling rack.

Step 7

Use a spice or coffee grinder to grind the poppy seeds into a powder. Transfer poppy seed powder to a medium bowl and add the sweetened condensed milk. Stir until fully combined. Cover and keep in the refrigerator until ready to use.