Combine boiling water and currants; let stand 15 minutes. Drain and set aside.
Trim crusts from bread; discard crusts. Cut each slice into 4 triangles; place triangles in a single layer in a 10-inch quiche dish coated with cooking spray. Pour 1/2 cup milk over bread; let stand 5 minutes. Top with currants, cheese, and grapes.
Place flour in a bowl, and gradually add remaining 1 cup milk, stirring with a wire whisk until blended. Stir in 1/3 cup sugar, cornmeal, lemon rind, egg whites, and egg; pour over tart. Drizzle oil over tart, and sprinkle with 1 tablespoon sugar and rosemary. Bake at 350° for 45 minutes or until set; let cool on a wire rack.