This cookie calls for everything and lacks nothing. Crispy, chewy, crunchy, chocolatey, fruity and nutty. It requires two bowls and a few minutes of time to throw it all together. The batter will be thick and it's best when you let it meld in the fridge for a few hours or overnight before baking. Store any uneaten cookies in a plastic bag or cookie jar for up to 3 days. Otherwise, toss them in the freezer for those moments when nothing but a crispy, chewy, good and good for you cookie will do.
Place racks in upper and lower thirds of the oven and preheat to 350 degrees.
Place nuts and oats on a rimmed baking sheet and put in the oven, tossing once, until golden brown, about 10-12 minutes. Transfer to a small bowl and allow to cool completely.
In a small jar, add the butter and melt it in the microwave. Add the brown sugar and granulated sugar and stir until the sugar melts.
In a medium bowl, mix egg, vanilla, salt and baking soda. Then, when the butter-sugar mixture has cooled slightly, add this to the egg mixture and stir well to incorporate.
When nuts are cool, add seeds, dried fruit and chocolate to the nut mixture and toss to combine.
Give the egg and sugar mixture another good stir and add the flour. Stir until combined to make a caramel-like mixture.
Add the nut mixture to the batter and stir completely so all of the ingredients are evenly coated with the batter. It will look like there are way too many mix-ins, but the dough will meld and melt together as it sits in the fridge.
Cover and chill at least 2 hours and up to 3 days.
When ready to bake the cookies, preheat the oven to 350 degrees. On two baking sheets, place parchment paper or a Silpat. Using an ice cream scoop, portion the dough into about 12-14 cookies. Press the cookies with your hands so they become 2 1/2"-diameter disks and about 3/4" thick. Sprinkle with flaky sea salt, if using.
Bake the cookies and rotate the baking sheets from top to bottom and front to back halfway during the cooking process. Bake about 11-13 minutes, until golden brown and no longer wet-looking. Let the cookies cool on the baking sheet.
Preserve any leftover cookies in a bag at room temperature for up to 3 days or store in the freezer.