Preheat your oven to 350F

For the poppy seed crust, combine the flour, melted butter, sugar, cornstarch, salt, and poppy seeds in a bowl and mix until all dry flour is incorporated and a dough forms. It will be slightly crumbly, but will hold together when pressed between your fingers.

Pat the dough into four mini tart pans with removable bottoms, and put the tart shells in the fridge for about 30 minutes.

For the filling, whisk the ingredients together well, making sure the eggs are thoroughly incorporated.

Pour the mixture through a strainer and then into the mini tart shells. (Note ~ before filling them, place your tart shells on a baking sheet, that way they'll be a lot easier to transfer to the oven. The baking sheet will capture any leaks that might happen during cooking, too.)

Bake for about 20-25 minutes or until the filling is cooked through. You should have a very slight wobble in the middle of the tarts, but nothing that still feels liquid-y. The shortbread tart shells should be lightly golden.

Let the tarts cool at room temperature completely in the tart pans, then remove the tarts from the tart pans, and top with powdered sugar when ready to eat.