2. Position the rack in the lower third of the oven.

3. Place the butter and both kinds of chocolate in the top of a double boiler set over simmering water. If you don't have a double boiler, place the butter and both kinds of chocolate in a heat-safe bowl that fits snugly over a small pot of simmering water. Stir constantly until half the Butter and chocolate is melted. Remove the top of the double boiler or the bowl from the pot; then continue stirring, away from the heat, until the butter and chocolate are completely melted. Transfer the mixture to a large bowl and allow to cool for 10 minutes. (To melt Butter and chocolate in a microwave, see pages 9-10.)

4. beat the remaining 1 cup sugar into the melted chocolate with a whisk or with an electric mixer at medium speed; continue beating until the mixture is smooth and silky, about 5 minutes by hand or 2 minutes with a mixer. beat in the remaining 2 eggs, 2 egg yolks, and 1 tablespoon vanilla until incorporated.

5. With a wooden spoon or a rubber spatula, stir in the flour and salt just until combined. Do not beat. Spread three-quarters of this chocolate batter into the prepared pan. Cover with the cream cheese mixture, spreading it as evenly as possible with a spatula. Do not press down. Dot the cream cheese mixture with the remaining chocolate batter, using heaping tablespoons of batter.

6. To create a swirl effect in the brownies, run a sharp kitchen knife through the batter without touching the bottom of the pan or lifting the knife up during its course. Slice through the chocolate dollops and drag some of the mixture into the cream cheese. Continue swirling until a spin-out, almost psychedelic pattern has formed.

7. Bake for 35 minutes, or until a toothpick or cake tester comes out clean. Set the pan on a wire rack to cool for at least 30 minutes.

8. Cut the brownies into 16 squares while they're still in the pan. Carefully remove them with an offset spatula. Serve immediately, or let cool completely before covering with plastic wrap for storage at room temperature. They will stay fresh for up to 4 days. The brownies can be tightly wrapped in wax paper, sealed in a freezer-safe bag, and frozen for up to 3 months; allow them to thaw at room temperature before serving.

To vary this recipe:
Substitute one of the following flavorings for the 1 tablespoon vanilla used in the chocolate batter:

• 2 1/2 teaspoons almond extract
• 2 1/2 teaspoons maple extract
• 2 teaspoons banana extract or 2 teaspoons coconut extract
• 2 teaspoons mint extract
• 2 teaspoons rum extract

and/or Stir in 3/4 cup of any of the following mix-ins, or 3/4 cup any combination of the following mix-ins, with the flour mixture in the chocolate batter:

• chopped candied chestnuts
• chopped candied orange peel
• chopped Heath® bars
• chopped Oh Henry!® bars
• chopped pecans
• chopped walnuts
• cocoa nibs
• dried cherries
• shredded sweetened coconut
• white chocolate chips