Preheat oven to 350 degrees F. Butter two 8-inch round cake pans. Line with parchment paper. Butter paper.
Spread 12 bread slices with 1 tsp. softened butter each; spread remaining 12 with 2 tsp. marmalade each. Sandwich slices with butter and marmalade facing. Trim crusts. Cut each sandwich into quarters diagonally; arrange in prepared pans, stacking and overlapping as necessary to fit snugly. In a small bowl stir together raisins, brown sugar, and cinnamon; sprinkle over top.
In a large bowl whisk together cream, condensed milk, and eggs. Pour over bread. Press bread down to absorb cream mixture. Bake 45 minutes or until a knife inserted in center comes out clean. Let cool 20 minutes in pans on a wire rack.
Meanwhile, in a small saucepan warm remaining marmalade over low heat.
Loosen sides of bread from pans. Invert one pan onto a platter; shake gently to loosen bottom. Remove parchment. Spread with half the warm marmalade. Invert second pan onto a baking sheet or wire rack, then invert again onto a rimless baking sheet so top faces up; gently slide onto first layer. Top with remaining marmalade. Serve within 2 hours. If desired, top with slices of blood orange, mandarin orange, and fresh rosemary sprigs.