Preheat oven to 400°. In a small saucepan over medium heat, add oil and shallot. Cook until shallot is soft and starts to brown, 5 to 7 minutes. Add blackberries, sugar, vinegar, and 2 tbsp. water. Simmer until thickened and jammy, 20 to 30 minutes. Season with salt. Place Brie in phyllo shells; bake until Brie is melted, about 5 minutes. Top with jam and garnish with pepper and mint.