Position a rack in the center of the oven and preheat to 325ºLine a rimmed baking sheet with parchment paper. Have a second rimmed baking sheet and piece of parchment ready.
Cook the butter in a medium saucepan over medium heat with the vanilla bean and scrapings, swirling the pan occasionally, until the butter browns and smells nutty, about 5-10 minutes. When the butter foams up, watch it closely so that it doesn't burn. There should be dark brown (but not black, save for the vanilla seedflecks of toasted milk solids on the bottom of the pan, and the butter should be golden in color. Let the butter cool slightly, then stir in the salt and maple syrup to dissolve the salt.
Combine the oats, nuts, maple sugar, cinnamon, and nutmeg together in a large bowl. Pour the butter mixture over the oat mixture, tossing to combine thoroughly, then stir in the bourbon.
Dump the mixture onto the lined baking sheet, and spread it into a thin sheet no thicker than an almond. Ideally, the edges will be slightly thicker than the center as they will bake faster. Lay the second piece of parchment over the granola, and place the second sheet pan on top, right-side up, making a granola sandwich of sorts.
Slide the whole thing into the oven and bake for 20 minutes. Rotate and continue baking another 10 - 20 minutes, peeking under the parchment to make sure the edges aren't burning, until the granola is a rich golden brown. It will still be soft, but will crisp up as it cools. (You can test for doneness by letting a small cluster cool on the counter. If it's crisp at room temperature, the granola should be good to go.)
Let the granola cool completely in the sheet pan sandwich, then break it up into clusters and store in an airtight container for up to a month or two. (If the granola is still soft when cool, no worries; break it up a bit and slip it, uncovered, back into a low oven, around 225ºF, until the granola is golden and crisps up when cooled. You can also revive stale granola this way.)
Enjoy this granola with milk and fresh fruit for breakfast, alone for a crunchy snack, or over ice cream for a decadent dessert. It makes a welcome gift, and will stay crisp in an airtight container for up to a month.Nutritional values are based on one of eight servings.