In a large mixing bowl, combine the all-purpose flour and fine sea salt, then mix in the melted unsalted butter until crumbly. Gradually add water, one tablespoon at a time, until a smooth, slightly sticky dough forms. Wrap in plastic wrap and refrigerate for at least 2 hours or overnight.

Peel and dice the russet potatoes, then place them in a pot of salted water. Bring to a boil and cook until tender, about 10-15 minutes. Drain the potatoes and set aside.

In a large skillet over medium heat, add olive oil and sauté the chopped yellow onion until translucent, about 4-5 minutes. Toss in the diced red and green bell peppers along with the frozen peas, cooking for another 3-4 minutes until soft. Add garlic, oregano, and spices, stirring until fragrant.

In the same skillet, add the ground beef and cook until browned, about 6-8 minutes. Mix in the drained potatoes, beef broth, and tomato paste. Season the filling with salt, pepper, and cumin to taste.

Preheat your oven to 400°F. On a lightly floured surface, roll out the chilled dough. Use a round cutter to cut out circles and place a spoonful of the beef filling in each. Fold the dough over, sealing the edges by pressing down and crimping with a fork.

In a small bowl, whisk together the egg and water to create an egg wash. Brush the tops of the empanadas with this egg wash.

Bake the empanadas for about 20-25 minutes or until golden-brown. Keep an eye on them to avoid over-baking.