Preheat oven to 350 degrees F (175 degrees C). Butter a 9x9 inch baking pan.
In a medium bowl, combine flour and 2 tablespoons brown sugar. Cut in butter until mixture is crumbly. Press into the bottom of the prepared pan.
Bake for 15 minutes in preheated oven. Crust should not be fully cooked.
In a large bowl, mix together the eggs and remaining brown sugar. Combine the oats, salt, and baking powder; stir into the egg mixture along with the vanilla. Mix in raisins and coconut, if desired. Spread the mixture evenly over the partially baked crumb layer in pan.