In a large bowl, mix the flour and salt. Cut in the butter until the mixture resembles coarse crumbs. Add the egg and water, and mix until a dough forms. Knead gently for about 5 minutes. Wrap in plastic wrap and refrigerate for 30 minutes.

Filling Preparation

Prepare the Picadillo Filling

In a skillet, sauté onion, garlic, and bell pepper until soft. Add ground beef and cook until browned. Stir in tomato sauce, olives, cumin, and season with salt and pepper. Simmer for 10 minutes.

Prepare the Spinach and Cheese Filling

In a skillet, heat olive oil and sauté garlic until fragrant. Add spinach and cook until wilted. Remove from heat and mix in ricotta, feta, and season with salt and pepper.

Prepare the Cuban Sandwich Filling

In a bowl, combine shredded pork, sliced ham, Swiss cheese, pickles, and mustard. Mix well.

Assembly and Cooking

Assemble the Empanadas

Preheat the oven to 375°F (190°C). Roll out the dough on a floured surface and cut into circles. Place a spoonful of one filling in the center of each circle. Fold over and crimp the edges to seal.

Bake the Empanadas

Place the empanadas on a baking sheet lined with parchment paper. Bake for 25-30 minutes or until golden brown.