14 tablespoons unsalted butter (1 3/4 sticks), divided
1 3/4 cups packed dark brown sugar (12 1/4 ounces)
2 cups plus 2 tablespoons unbleached all-purpose flour (about 10 1/2 ounces)
1/2 teaspoon baking soda
1/4 teaspoon baking powder
1 1/4 teaspoons cinnamon
1/2 teaspoon sea salt (table salt is fine, too)
1 large egg
1 large egg yolk
Heat 10 tablespoons butter in a deep medium saucepan over medium-high heat until melted, about 2 minutes. Continue to cook, stirring with a heat proof spatula until the butter is medium to dark brown and has a nutty aroma, 3 - 5 minutes. Remove pan from heat and transfer browned butter to a large heatproof bowl. Stir in the remaining butter into hot butter to melt; and set aside for 15 minutes.
Adjust oven rack to middle position and heat oven to 350 degrees. Line 2 baking sheets with parchment paper. Whisk flour, baking soda, baking powder, cinnamon and salt together in medium bowl and set aside.
Add the brown sugar to the bowl with the butter and mix until no sugar lumps remain, about 30 seconds. Scrape down the sides of bowl with a rubber spatula; add egg and egg yolk and mix until fully incorporated, about 30 seconds. Scrape down bowl. Add flour mixture and mix until just combined, about 1 minute. Give dough final stir with rubber spatula to ensure that no flour pockets remain and ingredients are evenly distributed.
Scoop out the dough into 24 portions, and set on prepared baking sheet, spacing dough about 2 inches apart, 12 dough balls per sheet.
Bake one sheet at a time until cookies are browned and still puffy and edges have begun to set but centers are still soft (cookies will feel well formed on the edge but centers will still be soft), 12 to 14 minutes, rotating baking sheet halfway through baking. Do not overbake.
Cool cookies on baking sheet 5 minutes; then transfer cookies to wire rack to cool completely (they are also delicious slightly warm).