How to Make It
Preheat the oven to 400°. On a rimmed baking sheet, toss the tomatoes with a teaspoon of the olive oil and season with salt. Roast the tomatoes for 20 minutes, until lightly browned in spots and softened.
In a blender, combine the flour, milk, water, egg, and 1/2 tablespoon of the olive oil. Pulse for 10 seconds until smooth. Cover and place the crêpe batter in the refrigerator to let rest for 20 minutes.
Meanwhile, whisk together the buttermilk, mayonnaise, 1 tablespoon of the olive oil, lemon juice, chives, parsley and salt and pepper until combined and set aside.
Preheat the oven to 350°. Heat a 10-inch nonstick pan and lightly brush it with some of the remaining olive oil. For each crêpe, add ¼ cup of the batter to the pan and quickly swirl to spread evenly. Cook over moderate heat until the underside is speckled and lightly golden, about 30 seconds to 1 minute. Flip the crêpe and cook for 30 seconds to 1 minute longer. Transfer to a baking sheet; repeat with the remaining batter to make 4 crêpes in total, brushing the pan with oil as needed.
Over a baking sheet, lay 1 ounce of the brie cheese slices over the center of each crêpe. Fold 3 or 4 sides toward the center overlapping slightly onto the cheese, and repeat with the others. Bake until the cheese is melted and hot, about 4 minutes. Transfer to plates and top with the frisée and roasted tomatoes. Spoon over the buttermilk dressing and serve right away.