2 cups old-fashioned oats
1 cup pecans, chopped
1 cup all-purpose flour
1 teaspoon kosher salt
½ teaspoon baking soda
½ teaspoon ground cinnamon
⅛ teaspoon freshly ground nutmeg
¾ cup (1½ sticks) unsalted butter, room temperature
¾ cup (packed) light brown sugar
¼ cup granulated sugar
1 large egg, room temperature
2 tablespoons pure maple syrup
2 teaspoons vanilla extract or paste
1 cup raisins, dried sour cherries, and/or dried cranberries
Preheat oven to 425°. Spread oats on a rimmed baking sheet and toast until lightly golden, about 6 minutes. Add pecans, toss to combine, and continue toasting until pecans are fragrant and oats are deep golden brown, about 6 minutes more. Let cool sightly.
Whisk flour, salt, baking soda, cinnamon, and nutmeg in a medium bowl; stir in oats and pecans.
Using an electric mixer on medium speed, beat butter, brown sugar, and granulated sugar in a large bowl, scraping down sides of bowl, until light and fluffy, 3–4 minutes. Add egg, syrup, and vanilla and beat until incorporated, about 1 minute. Reduce speed to low; add dry ingredients and raisins and continue to beat, scraping down sides and bottom of bowl, until just combined. Let sit at room temperature at least 1 hour to hydrate oatmeal.
Preheat oven to 350°. Line 2 rimmed baking sheets with parchment paper. Using a 2-oz. ice cream scoop, portion cookies and place on sheets, spacing 3" apart (or measure out mounded scoops with a ¼-cup measuring cup). Do not flatten; cookies will spread as they bake.
Bake cookies, rotating sheets halfway through, until edges are golden brown and firm but centers are soft, 15–17 minutes. Let sit on sheets 10 minutes, then transfer to wire racks; let cool.
Do Ahead: Cookie dough can be made 3 days ahead; cover and chill. Let dough come to room temperature before baking.