In a large mixing bowl, whisk together the all-purpose flour, sugar, and salt until well combined. Cut in the ice-cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs. Gradually add icy water, one tablespoon at a time, mixing until the dough comes together. Divide the dough into two discs, wrap in plastic, and chill in the refrigerator for 30 minutes.

Preheat your oven to 375°F (190°C). On a floured surface, roll out one disc of dough to about 1/8-inch thickness. Using a round cutter, cut into circles and gently press them into mini tart pans. Chill again for 15 minutes to firm up the dough. Bake the crusts for 10-15 minutes with pie weights until lightly golden and firm; let them cool completely.

In a saucepan over medium heat, bring the heavy cream to a simmer, then remove from heat. Add the chopped semi-sweet and milk chocolate to the cream, stirring until completely melted and smooth. Incorporate vanilla extract for extra flavor, and allow the filling to cool slightly before using.

Roll out the second disc of dough on a lightly floured surface to about 1/8-inch thickness. Use a shamrock-shaped cookie cutter to cut out fun shamrock shapes. Brush the tops lightly with an egg wash for a golden finish, or skip this for a vegan option. Bake these at 375°F (190°C) for 8-10 minutes until golden, then cool on a wire rack.

Once the mini crusts have cooled completely, carefully pour the chocolate filling into each crust until filled just below the rim. Place a baked shamrock on top of each pie, gently pressing it into the filling. Chill the assembled Chocolate Shamrock Pies in the refrigerator for at least 2 hours to set.