Lightly butter a 9 X 13 inch baking dish and lay the bread slices in the pan slightly overlapping each other. In a large mixing bowl, or the bowl of a stand mixer fitted with a whisk attachment, whisk together the creme fraiche, sugar, vanilla, cinnamon and nutmeg. Whisk until well combined. Add the eggs and whisk until incorporated. Slowly add the cream and milk, whisking slowly for a few minutes until the mixture is smooth and thickened slightly.
Pour the custard mixture over the slices of bread in the pan, being careful to moisten all the bread thoroughly. Sprinkle the fresh blackberries evenly over the French toast. Cover with plastic wrap and refrigerate overnight. Alternatively, you can leave the French toast out to soak while you preheat the oven, at least 20 minutes.
When you are ready to bake the French toast, preheat the oven to 400ºF. Remove the plastic wrap and spoon some of the custard mixture from the bottom of the pan over any of the bread that looks like it is still dry. Rearrange the berries to be evenly distributed then bake in the preheated oven for about 40 minutes, or until the edges of the bread just begin to brown.
While the French toast bakes, combine the berries for the syrup with the water and maple syrup in a small saucepan. Heat over medium heat for about 10 minutes. Remove from the heat and mash the berries with a potato masher or large wooden spoon to release all the juice possible. Return to the heat and continue to simmer for another 20 minutes or until syrup is thickened. Strain through a fine mesh sieve to remove all the seeds and serve warm with the French toast.
Serving Size 2 slices of French toast