Heat butter and brown sugar and bring to a boil. Remove from heat and stir in pecans. Set aside.
Grease a baking sheet with butter or cookin spray. Place bread slices on sheet and bake for about 5 mins. or until lightly toasted.
Beat milk, eggs, sugar and vanilla. Dip 8 slices of bread in batter and place on a baking sheet. Top each slice with heaping tablespoons of pecan mixutre. Dip 8 more slices in batter and place on top of nut filling to form a sandwich.
Bake for about 20 mins. or until hot. Dust with powdered sugar and serve hot.