Haven't made it yet -- maybe today or this weekend. Have some real work to get out of the way first.
I did rewrite the recipe to clarify it a bit for future reference. No changes in the cake itself, however, and Kim has blessed this version. Printable copy attached.
BTW, I usually melt chocolate in the microwave in a Pyrex measuring cup. Three ounces should take about 30 to 60 seconds; watch it carefully, take it out and stir it once it starts to melt, then return it for another 10 seconds or so; repeat as necessary, and remove from the microwave when there are still a few pieces left; stir until melted. The last few bits will melt as it sits. This way the chocolate is still pretty cool. Works with butter, too, or with chocolate and butter together.
KIM’S CHOCOLATE MARBLE CAKE
3 cups all-purpose flour [465 grams]
1 teaspoon salt [7.2 grams]
¼ teaspoon baking soda [1.7 grams]
1 cup sour cream [260 grams]
2 teaspoons rum extract [14 grams]
1 teaspoon almond extract [7 grams]
1 teaspoon vanilla extract [7 grams]
1 cup butter (two sticks) [226 grams]
3 cups sugar [603 grams]
6 eggs
4 ounces bittersweet chocolate [113 grams]
¼ cup + 1 tablespoon sugar [60 grams]
¼ teaspoon baking soda [1.7 grams]
¼ cup hot water (use just under ¼ cup) [55 grams]
1. Preheat oven to 325 degrees.
2. Grease and flour 12-cup Bundt pan and set aside.
3. Combine flour, salt, and baking soda, mix well, and set aside.
4. Combine the sour cream and the three extracts, mix well, and set aside.
5. Cream butter and sugar in electric mixer until light and fluffy.
6. Add eggs to butter mixture one at a time, mixing well after each addition.
7. Add the sour cream and mix to incorporate.
8. Add about ¼ of the flour mixture and mix until just absorbed; repeat, adding ¼ of
flour at a time, until texture is just smooth; do not over beat.
9. Divide batter into two equal portions.
10. Melt the chocolate.
11. Add sugar and hot water to melted chocolate and mix to incorporate.
12. When chocolate has cooled slightly, add baking soda and mix well.
13. Add slightly cooled chocolate mixture to one half of the batter and mix to
incorporate.
14. Put four large spoonfuls of the chocolate batter in prepared Bundt at the 12-, 3-, 6-,
and 9- o'clock positions, then add a layer of the white batter, then more of the
chocolate batter, repeating until all batter is added.
15. Optional: Run a knife around the pan one time to slightly swirl the batters together.
16. Bake for 80 to 90 minutes @ 325 degrees, or until cake begins to pull away from
pan and bounces back when pressed slightly in the middle.
17. Cool on rack for 20 to 30 minutes, then invert onto plate and remove pan. Allow to
cool completely before serving.