For the cheesecake swirl: Position an oven rack in the bottom third of the oven and preheat the oven to 325 degrees F. Combine the cream cheese, peanut butter, granulated sugar, sour cream and egg in a large bowl and beat with an electric mixer until well combined.
For the chocolate bread: Generously spray a 9-by-5-inch loaf pan with nonstick spray and dust with flour. Whisk the sour cream, oil, vanilla and eggs in a medium bowl. In another bowl, whisk the flour, granulated sugar, cocoa powder, baking powder, salt, and baking soda. Stir in the chocolate chips. Fold the wet ingredients into the dry ingredients.
Reserve 2 cups of the chocolate batter. Spread the remaining batter in the bottom of the prepared loaf pan. Spoon the cream cheese mixture over the chocolate batter and spread evenly. Spoon the reserved chocolate batter over the cream cheese mixture and spread to completely cover.
Bake until the top is cracked and a cake tester inserted in the center comes out clean, 1 hour 15 minutes to 1 hour 20 minutes. Cool on a wire rack for 30 minutes, then carefully invert onto a platter or cake stand and flip upright. Let cool completely, at least 1 1/2 hours. Dust with confectioners' sugar and serve.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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