Begin the night before you plan to serve. Preheat the oven to 350°. Place the hazelnuts on a baking sheet in a single layer and toast them until golden and fragrant, about 10 minutes. Pour them into a tea towel and rub to remove as much skin as possible. Place 1 C. of the nuts in a food processor with the sugar and whirl until the nuts are very fine. (Reserve the remaining nuts for the streusel.) Add the butter and one of the eggs to the remaining nuts in the processor and whirl until a smooth paste forms.

Spread a thin layer of the hazelnut butter on one side of the challah bread and place the slices, buttered side up in slightly overlapping layers in a greased 13” x 9” baking dish. Whisk the half and half, eggs, and almond extract until blended. Pour over the bread mixture. Place a sheet of foil on top of the pan and lay 2 cardboard juice or broth cartons on top to insure the bread is completely submerged. Refrigerate at least 6 hours, or overnight.

Make the streusel by coarsely chopping the reserved toasted hazelnuts and combining them with the brown sugar and butter in a small bowl. Rub the mixture with your fingers to create crumbles. Refrigerate.

One hour before serving, preheat the oven to 350°. Remove the weights and foil from the French toast, sprinkle evenly with the reserved streusel topping, and bake until it is set, puffed, and golden brown, about one hour. Meanwhile, prepare the Melted Blackberry Jam by combining the honey and jam in a saucepan and heating until melted. Stir in the lemon juice.

To serve, cut the French toast into squares and serve, passing melted Blackberry Jam separately .