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1
Heat 10 Tb butter in 10-inch skillte over mediem-high heat until melted, about 2 minutes.
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2
Continue to cool, swirling pan constantly until butter is dark and golden brown and has nutty aroma, 1 to 3 minutes.
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3
Remove skillet from heat and transfer brwoned butter to large heatproof bowl.
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4
Stir remaining 4 tb butter into hot butter to melt; set aside for 15 minutes.
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5
Meanwhile, adjust oven rack to mmiddle position and heat oven to 350 degrees.
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6
Line 2 large baking sheets with parchment paper.
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7
In shallow baking dish or pie plate, mix granulated sugar and 1/4 cup packed brown sugar, rubbing between fingers, until well combined; set aside.
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8
Whisk flour, baking soda, and baking powder together in medium bowl; set aside.
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9
Add remaining 1 3/4 cupes brown sugar and salt to bowl with cooled butter; mix until no sugar lumps remain, about 30 seconds.
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10
Scrape down sides of bowl with a rubber spatula; add egg, yolk, and vanilla until just combined, about 1 minute.
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11
Give dough final stir with rubber spatula to ensure that no flour pockets remain and ingredients are evenly distributed.
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12
Divide dough evenly into 24 portions, each about 2 tb, rolling between hands into balls about 1 1/2 inches in diameter.
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13
Working in batches, toss balls in reserved sugar micture to coast and set on prepared baking sheet, spacing them about 2 inches apart, 12 dough balls per sheet.
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14
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 look raw between cracks and seem underdone), 12 to 14 minutes, rotating baking sheet halfway through baking.
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15
Do not overbake.
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16
Cool cookies on baking sheet 5 minutes; using wide metal spatula, transfer cookies to wire rack and cool to room temperature.
