Using a sharp knife, split the vanilla bean in half lengthwise. With the back of the knife, scrape the pulp away from the bean. Discard the bean. In a saucepan, over medium heat, combine the milk, vanilla bean pulp, and 1/2 cup of the butter. Bring to a boil. Stir in the buckwheat and continue to cook until tender, about 20 to 25 minutes. Remove from the heat and cool. In a large mixing bowl, whisk the eggs and the sugar together. Stir in the cooled buckwheat mixture, lemon zest and raisins. Fold in the beaten egg whites. Butter a shallow baking pan (8 by 8 by 2-inch, square) with the remaining 2 tablespoons of butter. Pour the buckwheat mixture into the prepared pan. Bake in a preheated 350 degree oven for 30 minutes. Serve warm in individual serving bowls with cherry jam.