I am a big fan of America's Test Kitchen founded by Christopher Kimble. Their book, The Best of America's Test Kitchen, 2007, printed this recipe for Brown Sugar cookies. My family are all chocophiles but this is still their favorite cookie that I make. The browning of the butter does it! When you open the cookie jar, the smell of butter and brown sugar waft out and knock you over.
Adjust oven rack to middle and heat to 350 degrees F. Line 2 baking sheets with parchment paper or silicone mats.
Heat 10 tablespoons of butter in 10 inch skillet (not non-stick if possible, they make it harder to judge when butter is browned). Swirl melted butter over heat until it is dark golden brown and smells nutty, 1 to 3 min. Transfer butter to heatproof bowl. Add remaining 4 tablespoons of butter into hot butter to melt. Set aside for 15 min.
Combine granulated sugar and 1/4 cup brown sugar and a dash of salt in a shallow bowl. Set aside.
Whisk the flour, soda, baking powder,together in a medium bowl.
Stir the remaining 1 3/4 brown sugar and 1/2 teaspoon salt in to the cooled butter until evenly combined. Add the egg, yolk, and vanilla and mix until fully incorporated, about 30 seconds. Scrape down the sides of the bowl, add the flour mixture, mix until just combined, about 1 min.
Working with a small cookie scoop, 2 inches, or 2 tablespoons of dough, roll the dough into balls. Working in batches, roll the balls in the reserved sugars and place them on prepared baking sheets, about 2 inches apart.
Bake cookies, ONE sheet at a time, until browned slightly around the edges, set but soft in the center, rotating the sheet half way through the baking time. In my oven it is 11 minutes. Do not overbake as they become crisper when cooling. They do not look quite done. Bake only a few if you want to to try out your oven and timing. I always turn cookie sheets in the middle, all cookies.
Cool the cookies for 5 min. on sheet then transfer to a wire rack and cool to room temp. if you can! Bake next batch the same way, turning in the middle. The cookies keep 3 days in air tight container. We never get to the second day.