Preheat oven to 350 F. Butter bottom & sides of 4 (1-cup) mini bundt cake pans.
In a bowl, whisk together 1 1/4 cups flour, baking powder & salt. In a larger bowl, cream together butter & 3/4 cup sugar for about 2 minutes until light & fluffy. Add eggs & pure vanilla extract; stir to combine.
Alternately stir flour mixture & sour cream into the butter mixture, beginning & ending with the flour mixture, stirring well after each addition. Toss chopped rhubarb with remaining tablespoons of flour & sugar. Divide rhubarb evenly between the 4 mini bundt pans. Top evenly with cake batter
Bake cakes about 20 -25 minutes until golden & a toothpick inserted comes out clean. Remove from oven & invert on a cooling rack for a few minutes. Remove pans, replacing any of the rhubarb that has stuck to the pans.
Serve warm or cold with whipped topping or just a sprinkle of powdered sugar.