Make the Dough: In a medium saucepan over medium heat, add water and butter, heating until butter has fully melted. Meanwhile, in a large bowl, whisk together flour, salt, and paprika and make a well in the center.

Pour a little of the warm butter mixture into the well and mix with your fingertips to make a wet paste. Pour in remaining liquid, and work the dough with your hands until you get a wet, oily dough.

Wrap the dough in plastic and refrigerate for at least 2 hours. Preheat oven to 400°F and line a large baking sheet with parchment paper.

Prepare the Filling: Heat 2 tablespoons of oil in a large skillet over medium heat. Sauté the beef, cooking until browned, about 10 minutes. Remove the beef with a slotted spoon and set aside. Reserve 2 tablespoons of drippings.

With the remaining 1 tablespoon olive oil and 2 tablespoons of drippings, sauté the yellow onion until translucent, 10-15 minutes. Add the bell peppers, peas, garlic and seasonings.

After a few minutes, deglaze the pan with ¼ cup of beef broth, then add 1-2 tablespoons of tomato paste. Once dissolved, mix in the beef and potatoes. Remove from heat.

Assemble: Tear off golf-ball sized pieces of chilled dough and roll into balls. On a lightly floured surface, roll each ball into ¼-inch thick, 5-inch diameter circles.

Place 2 heaping tablespoons of filling in the center of each circle. Add ½ teaspoon scallions and sprinkle lightly with cheese if using. Beat egg and water together for egg wash.

Brush a small amount of egg wash along one half of the dough's edge. Fold over to create a half-moon shape and press edges firmly to seal. Crimp edges with the back of a fork.

Place empanadas on prepared baking sheet. Brush tops gently with egg wash. Bake until golden brown, about 20 minutes. Serve warm.