In a medium pot, heat the oil over medium high heat. (The mixture will bubble a lot so go larger than a saucepan for ease).
When the oil is warm, add the onion and cooked until soft and translucent, approximately 5 minutes.
Add the salt, black pepper, ground red pepper, and cornstarch and stir to combine. (Yes, this seems like a lot of salt and spice, but it works, I promise).
Add the Guinness, sugar, and honey. Let the mixture come up to a simmer and reduce heat to medium.
Let the sauce continue to cook and thicken until similar in consistency to heavy cream. This will take 30-45 minutes.
Pour into a jar or glass container and refrigerate after cooling slightly. Let it refrigerate ideally overnight to fully cool and thicken. The glaze will thicken much more when cool, and should then resemble the consistency of honey.
You can also use a full can, but the cans are larger in quantity. It will just take longer to reduce down as there is more liquid.When you put the glaze on something hot, it will thin out again so be careful when using on an open flame.If using for grilling, baking, etc, it is recommended to use the glaze at the end or when removed as the sugar in the glaze will easily burn.If reduced properly, this batch of glaze fits perfectly into a 16 ounce mason jar.