Before you heat treat and temper your plane iron, cut it to shape, because the untreated steel is much easier to cut and grind beforehand. There are a number of detailed articles online for the heat treating and tempering process, so here is just a brief rundown when working with O-1 tool steel.
I use one propane and one mapp torch (Why? Because that's the way I was taught). Clamp your steel in locking jaw pliers at an angle so that when you dunk it in the oil (I use peanut oil) and the oil flares up, you won't burn yourself. Position the blade in between the two flames, about 1" from both, so the blade is heated from both sides. Keep the blade moving so the heat is distributed equally across its width. Start heating the blade about 2" from the cutting edge. With a blade this thick and wide, it will take a while to get it hot enough (it took maybe 6 or 7 minutes). Once this part of the blade gets orange, start moving the flame toward the cutting edge until the entire 2" end is orange and glowing. Quench it quickly, dropping the blade straight down into the oil so the width of the blade is cooled equally, otherwise it may warp. The oil will flame for a bit. Keep moving the blade back and forth in the oil while it cools. I'd give it several minutes, then take it out, wipe it off, and let it cool enough for you to touch it.
Your blade will now be black. Before you temper it, you need to remove the black coating so that you can see the color of the blade as it's being tempered. You can remove the coating by rubbing the blade on a sheet of fine drywall screen or sandpaper that is resting on a reliably flat surface, like thick glass or granite.
Now you're ready to temper the blade. Bake at 350 degrees for an hour but keep an eye on it, as ovens temperatures vary. Other sources say 20 minutes at 400 degrees. When the blade becomes a straw color, it's done. Let it cool completely and you're ready for final sharpening.
You can get pretty technical with this whole process, and if you're a stickler for perfection or if you must have consistent and accurate results in making blades, you'll want to do more research than this post. But because I'm just a hobbyist, and chemistry and metallurgy make my brain hurt, this works just fine for my needs.
Here is another article on tempering steel, by Ron Hock, of Hock Tools.