Adjust two oven racks to the upper middle and lower middle positions. Preheat oven to 325 degrees. Line two rimmed baking sheets with parchment paper or foil.
In a very large bowl, whisk together honey, brown sugar, olive oil, vanilla, cinnamon, nutmeg, and salt.
Fold in oats, nuts, and seeds. Divide between two prepared baking sheets (about 7 cups granola per baking sheet) and spread evenly.
Bake 40 minutes, stirring the granola after 20 minutes. Remove from the oven and cool completely. Store covered in an airtight container at room temperature.
Honey: Substitute an equal amount of maple syrup if you prefer.
Olive oil: You can use a different neutral oil (grapeseed, avocado, canola, coconut) if you prefer.
Spices: I love cinnamon and nutmeg, but ground ginger, ground cloves, or allspice are all warming and fragrant too.
Rolled oats: Look for Old-fashioned rolled oats, not steel-cut.
Nuts and seeds: Choose raw nuts because they will be roasting in the oven. Pecans, pepitas (shelled pumpkin seeds), walnuts, cashews, hazelnuts, and almonds are all good choices. You can also add shredded coconut, chia seeds, or sesame seeds. I add these delicate ingredients halfway through baking, before I stir the oats, so they're perfectly toasted by the time the granola is done.
Maximizing clumps: For the clumpiest granola, use parchment paper to keep the sugar from sticking to the baking sheet. At the halfway baking point, use your spatula to push down on the granola after stirring, pressing the oats and nuts together. Also, let the granola completely cool on the baking sheet before breaking it up.
Knowing when it's done: Use your senses! Take the granola out of the oven when it is lightly toasty looking, evenly browned, and deliciously fragrant. For some batches, that may be a little longer than 40 minutes.
Storage: Keep the homemade granola in an air-tight container in the pantry for 4 to 6 months.
Orange zest: Zest a whole orange over the wet granola before baking.
Dried fruit: To keep it from turning rock-hard doing roasting, stir in dried fruit after the granola has cooled.
Chocolate: Chocolate chips or raw cacao nibs should be added to the granola after completely cooled.