Place 2 pounds of ground beef in a hot pan and break it apart.
Season the beef with 1 tablespoon of salt and cook until no longer pink.
Add the diced white onion and cook until translucent.
Add the diced Roma tomatoes and cook until they start breaking apart.
Add the diced yellow potatoes and cook, stirring occasionally, until the potatoes are soft.
In a blender, combine 3 tomatoes, ¼ onion, 1-2 serrano peppers, 2 garlic cloves, 1 teaspoon of salt, ¼ teaspoon of ground cumin, a big pinch of peppercorns or ground pepper, and 2 cups of water. Blend until smooth.
Pour the blended sauce into the pan with the beef and vegetables, stir, and cover. Simmer for 10-15 minutes, or until the potatoes are soft.
Serve the picadillo with sides like arroz rojos, quesadillas, and salsa verde.