Crust:

In a large bowl, stir together the flour, baking soda, and salt. 

In a separate large bowl, beat together the butter and sugar until light and fluffy. Beat in the eggs one at a time, and then mix in the milk, vanilla, and zests until combined. Add the dry ingredients to the wet ingredients in two batches, stirring well halfway through, until they are fully combined. Wrap the dough tightly in plastic and chill it thoroughly, for at least 4 hours but ideally overnight. 

This dough is very finicky; it’s best to let it chill thoroughly, ideally overnight, before you roll it out. Then it should be chilled in between steps to keep it sealed and beautiful throughout the baking process. 

Filling: 

In a spice grinder or coffee mill, finely grind the poppy seeds. In a saucepan over medium heat, cook the milk, sugar, dates, zests, and poppy seeds. Simmer them on low heat, stirring occasionally, until the seeds have absorbed the liquid and the mixture has thickened, about 15 minutes. Remove the pan from the heat and stir in the lemon juice, booze (if using), butter, and vanilla. Allow the mixture to cool completely. (This can be made ahead and stored in the fridge for up to 2 days, in an airtight container.) 

On a well-floured surface, roll the dough into a circle about 14 inches (35.5 cm) in diameter and 1/4 inch (6 mm) thick (you may have extra dough; just use it to make small hamantashen cookies with any extra filling or jams of your choice). Roll the dough back over your rolling pin to more easily transfer it to a parchment- lined baking sheet. Put the sheet in the fridge, uncovered, to chill the dough for 15 to 20 minutes. 

Remove the rolled dough from the fridge and spoon the mun (poppy seed mixture) into the center of the dough, leaving a 4-inch (10-cm) margin clear. Brush the edge of the dough circle all the way around with water or milk. Gently bring two sides of the dough together over the filling, pressing the edges firmly with the sides of your hands to seal them together This forms the top of your triangle. Then take the bottom edge of the dough and fold it inwards over the filling, pressing firmly to form the bottom of your triangle. You should be able to see the filling in the center. Go back over once more and firmly press with your palms to make sure the dough is well sealed along its seams. 

Return the galette to the fridge for another 15 to 20 minutes, during which time you can preheat the oven to 350 ̊F (175 ̊C). Brush the dough with egg wash or milk, and bake the galette for 30 to 40 minutes, until the cookie crust is golden. Allow it to cool completely, then dig in! 

The galette can be stored at room temperature for up to 3 days, in an airtight container.