Ingredients
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    2-2/3 cups 60% cacao bittersweet chocolate baking chips
    1/2 cup unsalted butter, cubed
    4 large eggs, room temperature
    1-1/2 cups sugar
    4 teaspoons vanilla extract
    2 teaspoons instant espresso powder, optional
    2/3 cup all-purpose flour
    1/2 teaspoon baking powder
    1/4 teaspoon salt
    1 package (11-1/2 ounces) semisweet chocolate chunks

Directions
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1. Preheat oven to 350°. In a large saucepan, melt chocolate chips and
   butter over low heat, stirring until smooth. Remove from heat; cool
   until mixture is warm.
2. In a small bowl, whisk the eggs, sugar, vanilla and, if desired,
   espresso powder until blended. Whisk into chocolate mixture. In another
   bowl, mix the flour, baking powder and salt; add to chocolate mixture,
   mixing well. Fold in chocolate chunks; let stand until mixture thickens
   slightly, about 10 minutes.
3. Drop by 1/4 cupfuls 3 in. apart onto parchment-lined baking sheets.
   Bake until set, 12-14 minutes. Cool on pans 1-2 minutes. Remove to wire
   racks to cool.