Preheat your Yoder Smokers YS640 to 425°F. Cut leeks crosswise into 1-2 inch rounds. Pack the rounds closely into an Lodge Logic 8” Cast Iron Skillet, cut sides up. You want a tight fit.
In a bowl, whisk together the heavy cream, asiago, half of the parmesan and the Cattleman's Grill California Tri-Tip Seasoning. Pour the mixture over the leeks until mostly submerged, cover with foil and bake for 45 minutes.
Remove foil and sprinkle remaining cheeses over the dish. Continue baking until leeks are tender and beginning to brown, about 30 minutes.