Step 1

Combine rhubarb, 1/2 cup sugar, and salt in a saucepan. Bring to a simmer over medium heat. Cook until rhubarb has broken down, stirring occasionally for 8 to 10 minutes. Place mixture into a bowl and place into the refrigerator to cool.

Step 2

Preheat the oven to 350 degrees and grease a 10-cup Bundt pan.

Step 3

Whisk flour, baking powder, salt, and baking soda together in a small bowl

Step 4

Cream butter, oil, and sugar together with an electric mixer in a large bowl until light and fluffy, about 3 minutes. Add eggs, one at a time, mixing well after each addition. Mix in vanilla extract. Add half of the flour mixture and mix until just combined. Pour in buttermilk and mix until just combined. Add in the remaining flour mixture and mix. Do not overmix.

Step 5

Pour half of the batter into the prepared Bundt® pan and smooth into an even layer. Remove rhubarb jam from the fridge, and carefully spoon over the batter. Place dollops of remaining batter over the jam and gently smooth it into an even layer, covering the jam completely.

Step 6

Place pan into the preheated oven and bake until a toothpick inserted into the center of the cake comes out with just a few moist crumbs, 55 to 60 minutes. Cool cake in pan for 30 minutes before running a knife around the edges to loosen. Invert the cake onto a plate and cool completely before serving.