1. In small saucepan, combine blueberries, sugar, cornstarch, lemon rind, allspice, cinnamon and salt. Bring to a simmer over medium-high heat; simmer, covered, 3 minutes or until berries have popped and mixture has thickened. Remove from heat.French Toast:
2. Slice ends off loaf. Slice loaf diagonally into 3/4-inch-thick slices (you should have about 18 slices).
3. In large bowl, whisk together eggs, half-and-half, rum, vanilla, salt, allspice and cinnamon. In 13 x 9 x 2-inch baking dish, place half the bread slices in single layer. Pour half of egg mixture over bread; press gently to submerge. Let soak 5 minutes.
4. Meanwhile, coat large nonstick skillet or griddle with nonstick cooking spray. Heat skillet or griddle over medium-high heat. Transfer soaked bread slices to hot griddle. Place remaining bread slices in baking dish and add remaining egg mixture.
5. Cook first batch of bread until golden brown, about 2 to 3 minutes per side (instant-read thermometer inserted in center of a slice should register 160 degrees F). Transfer French Toast to serving platter; cover with foil.
6. Cook second batch of French toast. Place on top of first batch. Dust with confectioners sugar, if desired. Serve immediately with warm Blueberry Sauce. Makes 6 servings.