Persimmon Walnut Bread Pudding

Name: Persimmon Walnut Bread Pudding
Ingredients: 1 lemon, zested; 1 cup mascarpone; 1 loaf challah, sliced 1/2-inch thick and toasted; 1 1/2 cups ripe persimmons, seeded and mashed (I used wild persimmons, but Fuyu make a fine substitute); Butter, for greasing the pan; Demerara sugar, for sprinkling; 3/4 cup walnuts, toasted and coarsely chopped; 1 cup heavy cream, for serving; 2 cups whole milk (use grass-fed if possible), divided; 1/2 cup spiced rum, divided; 3 eggs; 1/2 cup brown sugar; 1/2 teaspoon freshly grated nutmeg; 1/2 teaspoon cinnamon