Position a rack in the middle of the oven and preheat to 350 degrees F. Generously brush the bundt pan with shortening and dust with flour.
Whisk the flour, baking powder, baking soda and salt together in a large bowl and set aside. In another bowl, whisk the sour cream, lemon zest, lemon juice and vanilla and set aside.
Whisk the eggs and sugar together in another bowl, stirring vigorously to lighten the eggs. Gradually whisk in the oil until evenly combined. Add the sour cream mixture and stir together. Add the dry ingredients and stir with a wooden spoon just until combined but still a bit lumpy. Pour the batter into the prepared pan.
Bake the cake until it pulls away from the sides of the pan and a skewer inserted into the center of the cake comes out clean, about 1 hour. Cool 10 minutes; then unmold cake onto a rack placed over a baking sheet. Cool. (The cake can be prepared to this point a day ahead.)
When ready to serve. Combine the rhubarb, jam, water and salt in a small saucepan and simmer until the rhubarb gets translucent and syrupy, almost jewel like,, about 10 minutes. Add a bit more water, if the glaze gets too thick . Remove from the heat and stir in vanilla. Let cool slightly. Spoon some of the glaze over the top of the cake, and reserve the rest for serving with sliced cake. Serve.
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