Line a baking sheet with either a silicone mat (like this one), parchment paper, or foil. Preheat the oven to 300F degrees.
In a large bowl toss together the oats, brown sugar, cinnamon, and salt. If adding mix-ins that need/can be baked, like nuts, seeds, or shredded coconut, add them in here.
Either in the microwave (in a microwave-safe bowl) or on the stovetop (double boilers are the best things ever) melt the butter.
Combine the melted butter, honey, and egg white together.
Pour wet ingredients over oats, stirring until completely combined.
Transfer mixture to your prepared baking sheet and spread it evenly so that it is only 1 layer.
Bake for about 30 minutes. You will be able to tell when it is done when it looks just a little bit brown and toasty.
Cool completely on the baking sheet before transferring to an airtight container. During the transfer is when it will naturally break into huge clumps, feel free to break it up even more if you prefer your granola on the small cluster side.
If you somehow don't eat all of it in a day, it should keep for about 2 weeks in an airtight container at room temp.