Make your dough the day before you want your cookies. In a large bowl with a stand or hand mixer, blend butter and sugars until light and fluffy, about 2 minutes. You can do it by hand too if you like.
Then add vanilla, 1 egg and lime juice and zest and combine.
In a separate medium bowl, combine flour, ginger, cinnamon, all spice, baking powder and salt. Add to the wet ingredients and mix by hand just until combined. Dough should be slightly sticky.
Form dough into a large ball, flatten slightly, wrap with plastic wrap and chill overnight.
Then, make the lime curd!
Whisk together lime juice, zest, sugar, and eggs in a medium heavy-bottomed saucepan. Over low heat, stir in butter a little at a time, whisking often, for about 5-7 minutes or until curd is thick enough to coat the whisk. Careful not to turn the heat too high or the eggs may scramble. If you have some chunks in your curd, strain through a fine mesh strainer.
Transfer lemon curd to a bowl, cover with plastic wrap and chill for at least an hour or up to 1 week.
When you are ready to make your hamantaschen, preheat your oven to 350 degrees F and roll out the dough on a lightly floured surface until it thin, about ⅛ inch thick. Use a 3 or 3½-inch circle cookie cutter to cut circles in the dough. The top of a wine glass works too! Also helps with the drinking for Purim rule. Roll out the scraps and recut into circles.
Then take a teaspoon of the curd and put it in the center of each circle. Resist the urge to over-fill.
Fold two sides together overlapping at the bottom, and then fold the top down to make a triangle. Or pinch together sides.
Place on parchment-lined cookie sheets and freeze for 30 minutes to prevent spreading.
Brush with egg wash. Bake for 15 minutes or until lightly golden on the bottoms of cookies.
Cool on a cooling rack, though these are really good warm from the oven too or popped in the microwave for 10 seconds.