1, Preheat the oven to 325 degrees Fahrenheit with a rack in the lower third of the oven. Line an 8-inch square baking pan with two criss-crossed pieces of parchment paper, making sure that the paper is long enough to go up the sides a couple of inches. Grease the parchment paper. 烤箱预热到160度。在烤盘内铺上baking paper。

2, Brown the butter: Melt the butter in a medium-sized saucepan over medium heat. Continue to cook the butter, while whisking constantly, until it’s a pale golden brown and the particles suspended in it are reddish brown. This usually takes me about 10 minutes. 中火化黄油，直到变成淡淡的金黄色其中的颗粒程红褐色。大约10分钟

3, Remove the pan from heat and stir in the sugar. Then add the cocoa powder, sea salt, baking powder and espresso powder. Stir until the ingredients are thoroughly incorporated. Let the mixture cool for 5 minutes. 把锅拿起离火，放入糖进行搅拌。 然后加入巧克力粉，盐。 搅拌至所有配料都混合在一起，放一边凉5分钟。

4, Add the eggs one at a time, beating vigorously with a wooden spoon or silicone spatula after each one. When the mixture looks thick, shiny and well blended, add the vanilla extract and the flour. Stir until you no longer see streaks of flour. Then beat vigorously (put those arm muscles to work!) for 50 strokes with the wooden spoon or spatula. 鸡蛋一个一个加，用木勺用力敲打。当混合物看起来粘稠，有光泽后，加入香草精和面粉。搅拌至看不到面粉。 用力敲打搅拌50下。

5, Spread the batter in the lined pan, then use a knife to make light swirls in the top of the batter. Bake on the lower rack for about 25 minutes, until a toothpick inserted in the center comes out almost clean. Cool the brownies in the pan on a baking rack. 放入烤盘，烤25分钟。