Bring berries, 1/2 c. brown sugar, cayenne pepper, orange juice and salt to a simmer in a large, heavy saucepan over medium heat. Cook, covered, for 5 minutes.
Whisk together cornstarch and lemon juice in separate bowl; slowly add to berries, stirring constantly. Simmer for 1 minute. Add vanilla, turn off heat and let stand while making dough.
Mix together remaining 2 tablespoons sugar, the flour, baking soda, nutmeg, and 1/8 t. salt. Rub in butter using your fingers until very small pieces remain. Stir in milk until dough forms.
Return berry mixture to a gentle simmer over low heat, and add 6 mounds of dough. Cook dumplings on medium-low heat, covered, until cooked through, about 10 minutes. Remove pot. Serve warm.