In a saucepan over low heat, combine the butter and unsweetened chocolate. Heat, stirring often, until melted, about 4 minutes. Remove from the heat and stir in the sugar and salt. Add the eggs and vanilla and stir until well blended. Sprinkle the flour over the mixture and stir until just blended. Stir in the chips.
Pour the batter into the prepared dish and spread evenly. Bake until a toothpick inserted into the center of the brownies comes out almost completely clean, about 30 minutes (longer if using a metal pan). Do not overbake. Transfer the pan to a wire rack and let cool completely. Cut into 2 1/2-inch squares.
Makes 9 large brownies.
Adapted from
Williams-Sonoma Collection Series,
Dessert,
by Abigail Johnson Dodge
(Simon & Schuster, 2002).
