To make the orange blossom maple syrup, in a small saucepan over low heat, warm the maple syrup. Pour into a small bowl or pitcher and stir in the orange flower water and vanilla until well blended. Serve warm. Or, store in an airtight container in the refrigerator for up to 3 days. Warm over low heat before serving. 

In a bowl, whisk together the mascarpone, sugar, lemon juice and vanilla. Spread 2 Tbs. of the mascarpone mixture on 4 of the bread slices, leaving a 1/4-inch plain border on all sides. Top with the remaining bread slices. 

To make the batter, in a bowl, whisk together the eggs, milk, vanilla and salt. Pour the batter into a baking dish. 

In a large fry pan over medium heat, melt 1 1/2 tsp. of the butter and continue to heat until it foams but does not brown. 

Place each of the sandwiches in the batter and let stand for 5 seconds. Turn the sandwiches over and let stand for 5 seconds more. Using a wide spatula, carefully lift the sandwiches from the batter, letting any excess drip back into the baking dish, and transfer to the hot pan. Cook until browned, about 3 minutes. Add the remaining 1 1/2 tsp. butter to the pan, turn the sandwiches over and cook until browned on the other side, about 2 minutes more. Using a clean, wide spatula, transfer the sandwiches to a cutting board. 

Cut each sandwich in half on the diagonal. Divide among individual plates, top with the blackberries and serve immediately with the syrup. Serves 4.