Step 1: Prepare the Potatoes. Start by peeling and cutting the russet potatoes into thin fries to ensure they cook evenly and become crispier when fried. Rinse them thoroughly in cold water to remove excess starch, then pat them dry with paper towels.
Step 2: Coat the Fries. In a large bowl, combine all-purpose flour with Cajun seasoning, garlic powder, onion powder, paprika, salt, black pepper, and cayenne pepper if desired. Dip each fry into buttermilk before dredging it in the seasoned flour mixture.
Step 3: Fry the Fries. Heat vegetable oil in a deep fryer or large pot until it reaches 350°F (175°C). Fry the coated fries in batches for about 4-5 minutes until they turn golden brown and crispy; remove them from the oil and drain on paper towels.
Step 4: Top the Fries. While the fries are hot, sprinkle them with shredded cheddar and Monterey Jack cheese. Add crumbled bacon, sliced jalapeños, and chopped green onions.
Step 5: Serve Immediately. Serve the fries right away while they're still warm and gooey with melted cheese. Optionally drizzle some ranch dressing or your favorite dipping sauce over the top.