Step 1

Place 4 ounces cream cheese on the counter to soften at room temperature.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 350°F. Coat a 9x5-inch loaf pan with cooking spray. Line the pan with parchment paper, making sure the paper hangs over the 2 long sides.

Step 3

Finely chop 4 ounces dark chocolate. Place 2 ounces in a small microwave-safe bowl. Microwave in 30-second bursts, stirring between each burst, until the chocolate is smooth and completely melted, 60 to 90 seconds total; set aside for the fudge swirl.

Step 4

Place the remaining 2 ounces chopped chocolate, 1/2 cup Dutch-process cocoa powder, 1 cup packed dark brown sugar, and 1 teaspoon instant coffee or espresso powder granules in a medium bowl and stir to combine. Pour 1 cup boiling water and whisk until the everything is melted and smooth, about 1 minute. Set aside to cool for 5 minutes. Add 2/3 cup vegetable oil, 2 large eggs, 1/2 cup sour cream, and 2 teaspoons of the vanilla extract and whisk to combine.

Step 5

Place 1 1/2 cups all-purpose flour, 3/4 cup of the granulated sugar, 1 1/2 teaspoons baking powder, 3/4 teaspoon kosher salt, and 1/4 teaspoon baking soda in a large bowl and whisk to combine. Add the chocolate mixture and whisk just until smooth.

Step 6

For the swirl, place the cream cheese and the remaining 1/4 cup granulated sugar in a small bowl and stir vigorously until smooth. Stir in the remaining 1 teaspoon vanilla extract, 1 large egg yolk, and reserved melted chocolate until smooth and combined.

Step 7

Pour three-quarters of the cake batter into the prepared loaf pan. Drop all but 2 to 3 tablespoons of the cream cheese mixture by the tablespoon onto the batter. Drag a wooden skewer or table knife through the cream cheese dollops to make a swirled pattern. Top with the remaining cake batter. Drop the remaining cream cheese mixture onto the cake and swirl again with the skewer or knife.

Step 8

Bake until a skewer inserted into the center of the cake comes out with just a few moist crumbs clinging to it, 50 to 65 minutes. Place on a wire rack to cool completely before slicing.