These big chocolate and walnut chocolate chip cookies have a center filled with miniature marshmallows. The end result is a cookie marbled with chocolate and melted marshmallows. Lining the baking sheet with parchment paper makes these cookies easy to remove.
1/3 cup all-purpose flour
1/2 teaspoon baking powder
1/8 teaspoon salt
2 cups (12 ounces) semisweet chocolate chips, divided in half
2 tablespoons (1/4 stick) unsalted butter
1/2 cup sugar
1 large egg
1/2 teaspoon instant coffee powder dissolved in 1 teaspoon water
1/2 teaspoon vanilla extract
1/2 cup walnuts, coarsely chopped
60 (about 2/3 cup) miniature marshmallows
Preheat oven to 350 degrees F. Line 2 baking sheets with parchment paper. Stir flour, baking powder and salt in small bowl to blend. Set aside.
Stir 1 cup chocolate chips and butter in medium bowl set over saucepan of barely simmering water until melted and smooth. Transfer chocolate mixture to large bowl. Set aside.
Whisk sugar, egg, coffee mixture and vanilla in medium bowl until blended. Stir egg mixture into reserved chocolate mixture. Mix in flour mixture just until blended. Add nuts and remaining 1 cup chocolate chips.
For each cookie, drop 1 rounded tablespoon dough onto prepared baking sheet, spacing 3 inch apart. Gently press 5 marshmallows into center of each. Gently press 1 rounded tablespoon of dough atop each to cover marshmallows and form 2-inch-high mounds. Bake cookies until top is dull and feels crusty when touched gently, rotating baking sheets front to back and top to bottom halfway through baking to ensure even browning, about 14 minutes.
Cool cookies on baking sheet 15 minutes. Transfer to rack and cool completely.