Preheat oven to 350 degrees Fahrenheit.
In a large pot over medium heat bring rutabaga, carrots, onions, chicken stock, ¼ cup butter and brown sugar to a boil. Reduce heat and cook partially covered until vegetables are very tender (about 30 minutes). Remove vegetables, leaving liquid in the pot, and transfer to a food processor. Place a pan over high heat and boil the remaining liquid, stirring constantly until the liquid is reduced to about 1 tablespoon (about 2 to 3 minutes). Add the reduced liquid to food processor and puree until very smooth. Transfer to mixing bowl and allow to cool.
When mixture reaches room temperature stir in eggs, flour and baking powder. Season with salt and pepper and transfer the mixture to a casserole dish. Melt remaining butter and toss with chopped pecans. Sprinkle pecans evenly around the edge of the casserole to make a border.
Bake uncovered in preheated oven for about 30 minutes or until puffed, firm and golden brown.