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1
Position an oven rack in the center of the oven; preheat oven to 350.
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2
Lightly butter and flour a 9-inch fluted or plain tube pan and tap out the excess flour.
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3
Cake-in a microwave oven on Medium (50%) power, in a microwave-safe bowl, heat the chocolates together for 30-second intervals, stirring after each interval, until melted, about 2 minutes; let cool until tepid.
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4
In a bowl, whisk together the flour, baking soda, baking powder, and salt.
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5
In a large bowl, beat the butter and sugar with an electric mixer set on high speed until light and fluffy, about 3 minutes.
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6
One at a time, heat in the eggs, scraping down the sides of the bowl after each addition.
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7
With the mixer on low speed, gradually add the flour mixture, and then the sour cream and vanilla.
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8
Transfer half of the batter to a medium bowl.
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9
Add tepid chocolate mixture and chocolate chips and stir well.
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10
Add the orange zest to the plain batter.
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11
Spoon the batters alternately into the prepared pan.
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12
Using a table knife, swirl them together to create a marbled effect.
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13
Bake until a long bamboo skewer inserted in the center of the cake comes out clean, about 50 minutes.
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14
Let cool in pan on wire rack for 10 minutes.
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15
Meanwhile, make the syrup: in a small saucepan, bring the orange juice and sugar to a boil, over medium heat, stirring often to dissolve the sugar.
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16
Strain into a glass measuring cup.
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17
Invert the cake onto the cooling rack and unmold.
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18
Place the rack on a plate; slowly drizzle the orange syrup over the cake.
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19
Using a dessert spoon, retrieve the syrup on the plate and drizzle it back over the cake.
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20
Repeat until the cake absorbs all of the syrup.
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21
Let cool completely on the rack.
