Make the dough: In a large bowl, combine the All-Purpose Flour with a pinch of Salt and the Baking Powder. Cut cold Unsalted Butter into small pieces and rub it into the flour with your fingertips until the mixture resembles coarse crumbs.
Add one Egg and cold Water a little at a time, mixing until a soft dough forms; avoid overworking. Shape into a disk, wrap and chill for at least 30 minutes.
Preheat the oven to 200°C (395°F). Meanwhile, poach the Chicken Breast in simmering Chicken Broth until cooked through, about 12–15 minutes, then shred the meat and reserve about 1/2 cup of the cooking broth.
Prepare the filling: Heat Olive Oil in a skillet over medium heat and sauté the chopped Onion until translucent. Add minced Garlic and cook briefly until fragrant.
Stir in chopped Tomato and a spoonful of Tomato Paste, then add a Bay Leaf, a pinch of Sweet Paprika and freshly ground Black Pepper. Let the mixture simmer to concentrate the flavors.
Add the shredded chicken to the pan along with a splash of the reserved broth if the mixture seems dry. Fold in chopped Green Olives, Corn Kernels and Peas, and let everything heat through.
Finish the filling by stirring in chopped Parsley and a few spoonfuls of Requeijão Cremoso until the filling is creamy and well combined; adjust seasoning with more Salt or pepper to taste. Remove the bay leaf and let the filling cool slightly.
Assemble the pie: Roll out two-thirds of the chilled dough and line a greased pie dish. Fill with the cooled chicken mixture, spreading it evenly. Roll out the remaining dough for the top, cover the pie and crimp the edges to seal.
Make the glaze by whisking the Egg Yolk with a little Milk and brush it over the top crust for a shiny, golden finish. Cut a few small vents in the top to release steam.
Bake the empadão in the preheated oven for 25–35 minutes, or until the crust is puffed and deep golden. Let it rest 10 minutes before slicing so the filling sets.
Serve warm or at room temperature sliced into wedges; this empadão pairs beautifully with a simple green salad or roasted vegetables.
