Prepare the Potato Mixture:

1. Mix Base: In a large mixing bowl, combine cold mashed potatoes, 1 egg, grated cheese, softened butter, fresh herbs, garlic powder, onion powder, salt, and pepper. Mix until well combined and smooth. Taste and adjust seasoning.

2. Chill Mixture: Cover bowl and refrigerate for at least 30 minutes (or up to 24 hours). This firming step is crucial for easy shaping and prevents croquettes from falling apart.

Shape the Croquettes:

3. Portion and Shape: Using your hands or an ice cream scoop, portion potato mixture into 12-16 equal pieces (about 3 tablespoons each). Roll each portion into a cylinder or oval shape about 3 inches long and 1 inch thick. Place shaped croquettes on a parchment-lined baking sheet.

4. Chill Again: Refrigerate shaped croquettes for 15-30 minutes to firm up. This helps them hold shape during coating and frying.

Coat the Croquettes:

5. Set Up Breading Station: Place flour in first shallow dish, beaten eggs in second dish, and breadcrumbs in third dish. Line them up in order for efficient coating.

6. Bread Croquettes: Working with one croquette at a time: First, roll in flour, shaking off excess. Second, dip in beaten egg, letting excess drip off. Third, roll in breadcrumbs, pressing gently so crumbs adhere completely. Place breaded croquettes back on baking sheet. For extra-crispy coating, repeat egg and breadcrumb steps (double-breading).

Fry the Croquettes:

7. Heat Oil: In a large, heavy-bottomed pot or deep skillet, heat 2-3 inches of oil to 350°F (175°C). Use a cooking thermometer to monitor temperature—this is important for proper cooking.

8. Fry in Batches: Carefully lower 3-4 croquettes into hot oil (don’t overcrowd). Fry for 3-4 minutes, turning occasionally with a slotted spoon, until golden brown and crispy on all sides.

9. Drain: Remove fried croquettes with slotted spoon and drain on paper towels or a wire rack. Let oil return to 350°F between batches.

10. Serve: Serve hot immediately while crispy, with your favorite dipping sauces.