Dark and Dangerous Triple Chocolate Cookies

1 cup (250 mL) butter
1 cup (250 mL) granulated sugar
1/2 cup (125 mL) packed brown sugar
2 eggs
1 tsp (5 mL) vanilla
2 cups (500 mL) all-purpose flour
1/2 cup (125 mL) cocoa powder
1 tsp (5 mL) baking soda
1/4 tsp (1 mL) salt
1 cup (250 mL) semisweet chocolate chips
1 cup (250 mL) white chocolate or milk chocolate chips

Preparation:

Line rimless baking sheets with parchment paper or nonstick foil, or grease; set aside. In large bowl, beat butter with granulated and brown sugars until fluffy. Beat in eggs, 1 at a time; beat in vanilla. In separate bowl, whisk together flour, cocoa, baking soda and salt. Add to butter mixture, stirring to combine. Stir in semisweet and white chocolate chips.
Drop by heaping tablespoonfuls (15 mL), about 2 inches (5 cm) apart, onto prepared baking sheets. Bake in top and bottom thirds of 350°F (180°C) oven, rotating and switching pans halfway through, until firm to the touch and no longer glossy, about 12 minutes. Transfer to racks; let cool completely. (Make-ahead: Layer between waxed paper in airtight container and store for up to 5 days or freeze for up to 2 weeks.) Makes about 48 cookies

Source : The Complete Canadian Living Baking Book, 2008