Starter: mix all ingredients in a glass bowl. Cover loosely with lid or plate. Let stand in a warm place. Stir each day. On the 5th and 10th days add 1 cup flour, 1 cup milk and 1 cup sugar. Then remove 2 cups starter for restarting. (Keep 1 cup for yourself and give 1 cup to a friend.)
To the remainder combine all batter ingredients, mixing well. Pour half the batter into two greased and floured loaf pans (or one 9x13 pan). Mix streusel topping and pour half of it over the batter. Add the remaining batter, then the remaining streusel and bake at 350 for 40-50 minutes until the cake tests done.