Preheat oven to fries package directions. Line 2 baking sheets with foil and spray with cooking spray.
In a small bowl combine all the seasonings (NOT the ranch dressing). Lay the fries on the prepared baking sheet, dividing between the 2 trays. Sprinkle the seasoning over the fries on both trays. (Reserve ½ teaspoon seasoning for sprinkling on top of the fries during assembly, if desired)
Toss the fries to coat, making sure to end in a single layer.
Bake according to package directions, rotating the pans in the oven if needed.
To make the cheese sauce, while the fries bake, melt the butter in a medium skillet over medium low heat.
Add the flour and whisk together, cooking a minute or 2.
Slowly whisk in the milk until combined.
Let the sauce cook for a few minutes to thicken before slowly adding the cheese a little at a time to the sauce, letting each addition melt fully before adding more.
Reduce heat to the lowest it will go to keep the sauce warm but not cooking while getting the fries ready to assemble.
If the sauce is too thick, add an additional tablespoon or 2 of milk. The sauce will thicken as it cools so try to keep it warm.
To assemble, lay about ¼ of the fries on a plate and top with about ¼ cup of the cheese sauce. Drizzle with a tablespoon or so of ranch dressing then sprinkle with a bit of reserved seasonings, if desired.
Repeat for all the fries you want to use.
Serve immediately with more cheese sauce, ketchup and ranch for dipping, if desired.