The day before baking the cookies, Bring 2 cups of water to a boil in a medium sauce pan. Add the pepita seeds. Reduce heat and simmer for 5 minutes. Remove from heat, add baking soda and let sit overnight.
Rub the pepita seeds between your hands to remove the green skins. Drain the water from the pan while keeping the seeds in the bottom of the pot. Add more water and rub them again. Drain completely and place on a clean towel to dry.
In a mixing bowl beat the butter on medium speed until creamy, 2-3 minutes. Gradually add powdered sugar and the baking powder beat on low speed until incorporated scraping the bowl as needed, about 2 minutes.
Add the flour 1 cup at a time beating on medium until incorporated. Add egg yolks one at a time beating after each until it is incorporated. Add ½ cup warm water and beat until dough is smooth and can be formed into a ball. Wrap dough in plastic and chill for at least 30 minutes.
Preheat oven to 375℉. Line baking sheets with parchment paper or silicon baking mats.
Place half the dough between two sheets of waxed paper or parchment paper and roll out until ¼ inch thick. Using a 3 inch circle cookie cutter (or a glass) cut out the cookies and transfer to the baking sheet, about ½ inch apart.
Use a smaller circle cutter to make a slight indentation in the middle of each cookie. Press the tines of a from the inner circle out around each cookie.
Bake the cookies at 375℉ until golden brown around the edges, 13 to 15 minutes. Cool on the sheets on wire racks.
While the cookies are baking puree the dried pepitas in a food processor until they become a soft, smooth paste, about 5 minutes.
In a large saucepan combine granulated sugar mixed with ¼ cup water and cook over medium-low heat, stirring occasionally until the mixture is a light syrup, about 8 minutes. Stir in the pepita paste and cook for 3-4 minutes until the mixture is thick and shiny.Remove from the heat and stir in ¼ cup milk to make the mixture a bit more liquid.
Put a tablespoon of the pepita glaze in the center of one cookie. The glaze should spread to the inner circle and stop. If it doesn't spread on it's own add the remaining milk. Repeat with remaining cookies. Let stand until the tops of the filling are dry to the touch