• 1 stick (8 tablespoons) unsalted butter, cut into pieces
• 4 ounces unsweetened chocolate, chopped
• 1 cup sugar
• 3/4 teaspoon pure vanilla extract
• 1/4 teaspoon kosher salt
• 2 large eggs
• 2/3 cup all-purpose flour
optional: 3/4 cup chocolate chips
• 8 ounces cream cheese, well softened
• 1/3 cup sugar
• 1 large egg yolk
• 1/4 teaspoon pure vanilla extract
• Handful fresh raspberries
Put oven rack in middle position and preheat oven to 350°F. Butter an 8-inch square baking pan. Heat butter and chocolate in a 3-quart heavy saucepan. Remove from heat, cool for a few minutes. Stir in sugar, vanilla, and salt. Add eggs and stir until well combined. Stir in flour until just combined and spread in baking pan.
Make cheesecake batter: Whisk together cheesecake batter ingredients in a small bowl until smooth. Dollop over brownie batter, then swirl in with a butter knife.
Sprinkle raspberries over pan. Bake until edges are slightly puffed and center is just set, about 35 minutes.