Preheat oven to 350°F (175°C). Line a loaf pan with parchment paper and spray with cooking spray. In a bowl with an electric mixer, mix the coconut oil and clear vanilla. Add the sour cream and beat until combined. Add the sweetener. Add the egg whites one at a time, mixing after each. Stir in the flours, baking powder, and salt until thoroughly combined. Spread in the prepared pan. Bake at 350°F (175°C) for 35-40 minutes. The center should be set and not jiggly. Cool completely. For the glaze, stir together the glaze ingredients until smooth. Transfer cake to a serving platter and drizzle with the glaze.