Preheat oven to 250°F. Line 2 rimmed baking sheets or sheet pans with parchment paper.
In a saucepan over medium heat, combine the butter, brown sugar, and honey. Cook, stirring occasionally, until the butter is melted and the mixture comes to a full boil. Remove the saucepan from the heat and stir in the vanilla.
In a large bowl, combine the oats, salt, and any nuts, seeds, or flavor boosters you’re using.
Pour the hot syrup mixture over the oats. Stir thoroughly, scraping the bottom of the bowl as you mix, until all of the oats are evenly coated.
Divide the granola evenly between the prepared baking sheets. Spread it into a thin, even layer and gently press it down with a spatula.
Bake at 250°F for 1 hour without stirring.
Remove the pans from the oven and let the granola cool completely without stirring. The coating will firm up as it cools and create crunchy clusters.
Once completely cool, break the granola into pieces and stir in up to ½ cup of your favorite sweet mix-ins, if using.