1. **Prepare the Dough:**

– In a large bowl, combine the sifted flour and salt.

– Add the cold, diced butter and mix with your fingers until the mixture resembles coarse crumbs.

– Add the egg yolk and mix until the dough starts to come together. If necessary, add cold water, one tablespoon at a time, until a smooth dough forms.

– Shape the dough into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

2. **Prepare the Filling:**

– In a skillet over medium heat, heat the olive oil.

– Add the chopped onion and sauté until translucent.

– Add the minced garlic and cook for another minute.

– Stir in the diced tomatoes and cook until they soften.

– Add the chopped hearts of palm and cook for a few minutes.

– Sprinkle the flour over the mixture and stir well to combine.

– Gradually add the milk, stirring constantly until the mixture thickens.

– Stir in the chopped parsley and season with salt and pepper to taste.

– Remove from heat and let the filling cool completely.

3. **Assemble the Hand Pies:**

– Preheat the oven to 350°F (180°C).

– On a floured surface, roll out the dough to about 1/8-inch thickness.

– Cut out circles large enough to fit into muffin tins, reserving some dough for the tops.

– Press the dough circles into the muffin tin cups.

– Fill each cup with the cooled hearts of palm mixture.

– Cover each pie with a smaller dough circle, sealing the edges by pressing them together.

– Brush the tops with beaten egg.

4. **Bake:**

– Bake in the preheated oven for 30–35 minutes, or until the pies are golden brown.

– Allow to cool slightly before removing from the muffin tins.