In a large bowl, whisk together eggs, 3 cups of cream, milk, brown sugar, butter, vanilla, cinnamon, nutmeg, and salt. Fold in bread and let stand 30 minutes at room temperature. Stir occasionally.
Meanwhile, whisk together amaretto and cornstarch in a small bowl. In a medium saucepan, heat 1 1/2 cups cream over medium-high heat. Cook until hot, about 5 minutes. Whisk in amaretto mixture and bring to a boil. Lower heat and simmer for about 2 minutes, until thickened. Remove from heat and whisk in sugar. Set aside.
Preheat oven to 350 degrees and grease a 9x13-inch baking dish with butter.
Mix white chocolate, and all blueberries into bread mixture.
Pour mixture into prepared dish and sprinkle almonds on top.
Bake for 1 hour, or until set. Let cool 20 minutes before serving with amaretto cream.
Notes
You can bake in several smaller baking dishes (I used mini pie pans) or individual sized ramekins. Adjust the baking time down since they will cook faster. The amaretto cream can be made a day or 2 in advance and refrigerated.