Preheat oven to 375°F (190°C). Grease a 12-cup muffin tin with butter.

For the dough: In a large mixing bowl, combine flour and salt. Cut in cold butter using a pastry cutter or fork until mixture resembles coarse crumbs.

Add eggs and milk gradually, mixing until dough comes together. Divide dough into two portions, wrap in plastic, and refrigerate for 15 minutes.

For the filling: Heat olive oil in a skillet over medium heat. Sauté onions and garlic until softened, about 5 minutes.

Drain and chop hearts of palm into small pieces. Add to the skillet and cook for 3 minutes.

Stir in cream cheese and heavy cream. Season with salt, black pepper, and parsley. Cook until mixture thickens, about 5 minutes. Remove from heat and let cool slightly.

Roll out dough on a floured surface to 1/8-inch thickness. Cut circles to fit muffin cups, pressing dough into each cup.

Fill each pastry cup with the palm heart mixture, leaving space at the top.

Roll out remaining dough and cut circles for tops. Place over filling and press edges to seal. Cut a small slit in each top.

Brush tops with beaten egg yolk for golden color.

Bake for 20-25 minutes until golden brown. Let cool for 5 minutes before removing from tin.