Hi! Santa left a Rome cast iron waffle maker in my stocking this year (poor, stretched-out stocking! The beast is small but heavy). I Googled relentlessly, since this is <blush> my first cast iron experience (non-enameled, of course).
The Rome comes with a protective wax coating, which must be melted before the iron can be seasoned. I ended up separating the plates and sticking them on barbecue outside (with lid closed), med-high heat, for about 15 min each side, then turned it off and let cool. This was my method of choice to avoid a smoky kitchen.
To season the iron, I coated each side evenly (not too thick) in Earth Balance shortening, and placed each piece, grate-side down, on a foil-lined pan. I baked for an hour at 350º, then let cool. I repeated this process twice. As expected, the iron went from a pretty gun-metal grey to a brownish black.
I've since used the iron multiple times, and am very happy with the type of waffles produced (on the thinner side, with crispy edges! my fave). I've experimented with cooking spray, as per Vegan Brunch (blech - nasty chemically smell when it hit the iron, for some reason), Earth Balance shortening (waffles stuck each time), and even a brushing of canola oil - each with varying results.
My current method of success is:
1) separate plates and heat (grate-side up) on separate burners (I used medium-ish heat on my gas stove, or about a 4). A few droplets of water will dance when the iron is hot.
2) brush both grates with coconut oil (the solid kind - I loosened up some shards with a knife, then dipped in my silicon brush) - ensuring each nook and cranny gets a little coconut oil love.
3) Poor batter from a glass measuring cup (the one I used to mix the ingredients) onto one of the grates (which becomes the "bottom" of the iron), leaving about an inch or so "border" for the waffle to spread
4) USING HEAVY DUTY OVEN MITTS (the iron is HOT), re-attach the other plate and close iron, so this plate becomes the "top" but is already hot from the separate heating
5) set timer for 3 minutes, then (using said oven mitt!) flip and cook for another 3 minutes - then carefully peek/check to see if waffle has sufficient browning. It seems that the more my iron is seasoned from use, it's needed a bit longer browning, or a little nudge higher in temp.
--->your stove may be different, of course - so carefully monitor your first few attempts to adjust temp or time. The only times I've had waffles stick or come out too dark have been when I used something other than the coconut oil, OR did not use enough batter.
It's definitely a work in progress, and will take a bit of expertise before I can rest at ease and make them like second nature (although I did have the iron running yesterday morning, whilst making a mushroom scramble, and was comfortably manning both pans with relative ease). That said, I've now made the Vegan Brunch Chelsea Waffles several times, and my omni family ADORES them. Better than any waffles I can buy in these parts. In fact, just had a leftover one from the toaster - still sooooo scrumptious.