In a medium bowl, melt the butter and let come to room temperature. Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper. Spread the pecans in a single layer on a separate baking sheet. Roast in the oven until fragrant and toasted, about 8 minutes. Set aside to cool. In a large bowl, combine the flour, baking soda, salt, cinnamon, and nutmeg. To the bowl with the melted butter, add the brown sugar, egg, egg yolk, and vanilla. Whisk briskly until well combined. Pour the wet ingredients into a bowl with the dry ingredients. With a rubber spatula or wooden spoon, stir to combine. Stir in the oats, raisins, and walnuts. If your dough is too soft to scoop, refrigerate it for 20 to 30 minutes (or for optimum texture refrigerate a few hours. That said you can proceed right away and still have really delicious cookies!). With a cookie scoop or spoon, portion the dough by 1 1/2-tablespoonfuls and roll into a ball (the balls will be about 1 1/2 inches wide and you will have about 22 cookies). If the dough sticks to your hands, very lightly moisten them with water. Place the balls on the parchment-lined cookie sheet, leaving an inch of space between them. Refrigerate the bowl with any unscooped cookie dough until you are ready to finish the following batches Bake oatmeal cookies for 10 minutes, until they are golden on the top and edges, but still look underdone in the center. Let rest on the baking sheet for 5 minutes, then transfer to a rack to cool completely (or for as long as you can stand). Repeat with remaining cookie dough, ensuring that you let the baking sheet cool completely between batches or the cookies will spread.