Hi funknugget

I've made, stored and successfully used canna butter that's been almost a year old.
Do you know if it was made using regular butter, or from something like clarified (ghee) butter, coconut oil etc?
The clarified types are made by skimming out the water and milk impurities when heating and therefore, can last for a couple of years in the fridge as they won't go off. If in doubt they are also ok to freeze.

Assuming what you have is made from regular butter you'll need to use it sooner rather than later as you run the risk of it turning rancid, but a good brownie mix will disguise much of the flavour anyhow.

Good luck, and happy baking.