Find a large chefs knife to chop up the whole pineapple. First, trim about 1/2 inch off the bottom of the pineapple. Stand up the fruit on the cut end so that it nice and stable on your cutting board. Hold the top leaves and cut the hard outer surface off. Make sure you go deep enough to get all of the brown divit bits from the skin because they do not soften well, even after cooking. One the pineapple is peeled, cut the top off and then quarter length wise. Cut the hard core pieces out and slice into roughly 1 inch chunks. In batches, add the pineapple to a blender and puree.
Set a large heavy bottomed fry pan over medium heat and add the puree to the pan. Stir continuously and simmer for about 30 minutes until the pineapple begins to dry out and become sticky. Add the sugar and lemon juice and stir to combine. Continue cooking another 10-15 minutes until the filling gets sticky and turns a light caramel brown color. Remove from pan to cool and then store in the refrigerator for at least 30 minutes. A large metal mixing bowl works well for this to help it cool faster.
If you have time, leave the butter out for a while to let it soften or quickly soften it in the microwave for 10-20 seconds (this is not ideal because it will be a little warm, but sometimes you just gotta get cooking). Whisk together the butter and condensed milk to cream together. Add in the egg yolks and whisk to combine. Mix in the flour slowly and combine to make the pastry dough. The dough is done when it is no longer sticky. If it seems too soft or sticky, you can chill it in the fridge for a while before creating the tarts. Once your pineapple filling is cool, you can start to create the tarts.
Creating the Pineapple Filled Tart Cookies - Pre-heat oven to 350°F. Cover a large baking sheet with parchment paper, find some food-safe plastic gloves (helpful, but not totally necessary) and a friend to help. While wearing gloves scoop out a 1 inch ball of dough and then smash into your palm to form a circle. Have your friend scoop about 1/2 teaspoon of filling onto the dough circle. Close the hand holding the dough circle to encase the filling with dough. It will seem messy and not too well covered, not to worry! Gently roll the rough ball shape between your palms and the dough will come together. Often some filling will show through, also not a worry. Place onto the baking sheet and repeat and repeat until you run out of dough. Typically we have some filling left over, but you can eat for a snack later.
Once all of the cookies are filled and placed on the baking sheet, score the tops gently with the blunt side of a knife to create a crisscross pattern. Use a pastry brush to coat the top of each cookie with the egg wash. If you have some left after going over each one, you can add an additional coating. It will look eggy and funky, but it makes a beautiful toasted color on the finished cookie.