Add the rice to the casserole and cook, stirring, for 2 minutes. Add 1 cup of the warm stock to the rice and cook over moderate heat, stirring, until the stock is nearly absorbed. Continue adding the stock 1 cup at a time, stirring constantly, until the rice is al dente and a thick sauce forms, 22 minutes. Stir in the cooked beets, cheese and the 2 teaspoons of poppy seeds. Cook, stirring, until heated through; add a few tablespoons of water if the risotto is too thick. Spoon the risotto into bowls. Garnish with sliced beets and poppy seeds and serve.