Preheat oven to 250 degrees.
Put the peas in an oven-proof bowl, cover with a plate and put in the oven.
Cut the onion into 1/2 inch pieces and cook in butter until just transparent. Add to the peas.
Cut the potatoes into 1-inch chunks and cook in water with up to 1/4 cup coarse salt until a toothpick penetrates. Drain and add to the peas
Make a rue with butter and flour. Add milk, bullion concentrate, pepper and dill. When thick, add to the peas, stir and serve.