To do this yourself, you will need a love of fine food and a sound understanding of electrical wiring. Materials needed are an old-fashioned non-computerized electric range, a temperature controller, a scrap electric cord with plug, and household electrical kit.
Step 1: De-energize the Stove
Step 2: Identify the Right Wires
Now, lift the stove deck and identify the unique color of the wires feeding the target burner. These happen to be blue. That's it: Close it up, you're done here. The burner should not be modified in any way.
Step 3: Access the Infinity Switch
My object was not to replace the switch, but completely disconnect it from the stove power supply. I also disconnected the switch from the indicator light, which was tied to the adjacent switch. The blue wire electrical connections between the burner and switch stay put.
Step 4: A Kinder Gentler Source of Power
This switch works correctly with half the original voltage, but now delivers half the current to the burner at any particular setting. Which is better for low-temp cooking.
Everything I'm doing here is reversible in minutes.
Step 5: Temperature Control
The new 120 volt stove line is plugged into the temperature controller outlet.
At HIGH, the burner will now draw about 300 watts of electricity. But only when the controller calls for heat. At the cooking temperatures I need to maintain, this happens 6 to 12 seconds per minute. So the burner is delivering the equivalent of continuous 30 to 60 watts of heat to the pot. That's what I use for all the LED kitchen lighting. It's fantastically efficient.
When the new stove line is unplugged, this switch and burner is completely de-energized. The rest of the stove behaves normally.
Update: Jah3 spotted an error. With half the voltage and half the current, the burner will deliver a quarter of the watts. Originally delivering a maximum of 1200 watts, the burner is now limited to 300 watts. Correction: On MEDIUM, it will give me about 150 watts, or the controlled equivalent of continuous 15 - 30 watts. Which is enough to maintain the cooking temperatures I need.
Step 6: Why? Why? Why?
See that back burner? I never even used it. I only have 2 hands, and 4 burners is functional overload for me. This burner will precisely heat various water bath vessels (formerly known as pots) from 1 quart to 5 gallons. No turkey can stop me now. Plus there is no gadgetry to clutter my precious little counter space.
Goodbye crockpot? No, since the stove simply unplugs from the temperature controller, I can still Dork it and any other switchable countertop appliance.
Step 7: Results
Bon appetit from Sarasota
Step 8: A Few Words on Safety
The simple USDA guides for safe food temperatures are based on high delta T cooking. That is to say, the temperature of the cooking medium is much higher than the target internal food temperature. For example, if you cook pork in 350F air, you must limit the cooking time to get an internal meat temperature of 145F. This results in temperature/texture/visual/flavor gradients in the food.
With Zero Delta T cooking methods, there is no temperature difference between the cooking medium and the cooked food. Meat can and must be cooked longer at lower temperaturesfor pasteurization. However, longer cooking times generally lower the internal temperatures needed for pasteurization. This often improves flavor and texture. Whenever you cook to lower internal temperatures than USDA recommended, use the more complicated time/temp tables available online to be safe.
If you experience a power failure of unknown length during unattended cooking, you really can't tell if the resulting food will be safe to eat. So it should be tossed. It is foolish to tempt food poisoning. Many people get sick and die from this every year. If you are uncertain about any of this, call the USDA Meat and Poultry Hotline at (888) MPHotline. They have the last word on food safety.
Cody pointed out in comments that a displaced temperature probe could cause runaway heating. I completely agree and should have addressed this possibility.
If the probe falls out of the pot, the controller may deliver continuous heat which could boil the pot dry. That could lead to smoking food and a pot meltdown and stove damage or worse. While this is unlikely, we should actively prevent the problem with unattended cooking. First, secure the probe in open water inside the pot with a bend or loose knot or something. Then turn down the burner switch to the lowest setting that will maintain cooking temperature. Longer heating cycles with less current creates a more stable water bath and is better for the controller anyway.