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1
Whisk together the flour, baking powder and salt in a small bowl.
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2
Melt the chocolate chips and butter in a medium microwave-safe bowl in the microwave in 30-second increments, stirring in between, until smooth.
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3
Let cool slightly.
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4
Beat the sugar and eggs with an electric mixer on medium-high speed in a large bowl until thick and pale yellow, about 2 minutes.
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5
Scrape the chocolate mixture into the egg mixture and beat until incorporated.
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6
Beat in the vanilla.
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7
Add the flour mixture and beat on medium-low speed.
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8
Fold in the walnuts if using.
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9
The batter will be quite soft at this point.
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10
Refrigerate until firm enough to scoop, about 30 minutes.
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11
Position oven racks in the top and bottom thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper.
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12
Scoop heaping tablespoons of batter (a number-30 ice cream scoop works great, too) onto the prepared baking sheets about 2 inches apart (the cookies will spread considerably).
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13
(You will have additional batter for a second batch.)
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14
Bake until the tops of the cookies are crackled and no longer glossy and the edges are firm, 14 to 16 minutes, rotating the sheets about halfway through.
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15
Let the cookies cool for a few minutes on the baking sheets, then transfer them to a wire rack to cool completely.
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16
When the baking sheets are cool, repeat with the remaining batter.
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17
The cookies can be stored in an airtight container at room temperature for up to 3 days.
