• Preheat oven to 350F and position oven rack in the center of the oven.

  Lightly butter and flour a 9-inch fluted or plain tube pan and tap out the excess flour.

  Or, generously spray the cake pan with a baking non-stick spray such a Baker's Joy.

For the cake:

• Melted the chocolate in a microwave proof bowl in 30-second intervals, stirring at each interval, until melted; about 2 minutes. Let cool until tepid.
• In a medium bowl, whisk together the flour, baking soda, baking powder and salt.
• In a large bowl (or in a stand mixer), beat the butter, and sugar with an electric mixer set on high speed until light and fluffy, about 3 minutes.
• One at a time, beat in the eggs, scraping down the sides of the bowl after each addition.

  With the mixer on low speed, gradually add the flour mixture then the sour cream and vanilla (and Sweet Buttery Dough Flavor, if using).
• Transfer half of the batter to a medium bowl. Add the tepid chocolate mixture and chocolate chips (if using) and stir well.
• Add the orange zest (and orange oil, if using) to the plain batter.
• Spoon the batters alternately into the prepared pan. Using a table knife, swirl them together to create a marbled effect.
• Bake until a long bamboo skewer inserted into the center of the cake comes out clean-- between 40 and 50 minutes (depending on your oven). Let cool on a wire cooking rack for 10 minutes.

For the syrup:

• In a small saucepan, bring the orange juice and sugar to a boil over medium-heat, stirring often to dissolve the sugar. Strain into a glass measuring cup.
• Invert the cake onto the cooling rack and unmold. Place the rack on a plate (or baking sheet). Slowly drizzle the syrup all over the cake.

  Use a dessert spoon to scoop up any remaining syrup and drizzle it back over the cake.
• Let the cake cook completely on the rack.