Preheat the oven to 325°F and place the rack in the middle position. Prepare a 12-cup Bundt pan by spraying generously with nonstick baking spray.
In the bowl of your stand mixer fitted with a whisk attachment, add butter and sugar, and mix for 6 minutes on high speed until pale and fluffy.
Add the eggs, and mix well after each addition, scraping down the sides and bottom of the bowl.
In a medium bowl, whisk together flour, salt, and baking soda. Reduce the speed of the mixer to low and add dry ingredients.
Add the sour cream, oil, and vanilla and mix until just combined. Do not overmix.
Evenly separate the batter into three medium bowls. Set one bowl aside; this will be the vanilla batter.
Fold cocoa powder into the batter in the second bowl until evenly combined. Set aside.
To the third bowl, add the melted jam, extract, and food coloring, if using. Set aside. The strawberry batter will be thinner than the rest of the batters due to the extra liquid, but that is fine.
Alternate dollops of each batter into the prepared pan and use a knife to swirl the batters together.
Place cake in the oven and bake for about 1 hour 5 minutes, until an inserted toothpick comes out mostly clean and the edges of the cake have browned lightly and begun to pull away from the sides of the pan.
Remove from the oven and cool in the pan for 15 minutes. Then invert onto a wire rack to cool completely, about 1 hour.
Once the cake is completely cool, dust lightly with powdered sugar.