Steps
1. Preheat the oven to 350°F (175°C).
2. Line the bottom of a small (4-inch) round pan with waxed paper and spray the sides with cooking spray.
3. Microwave the chocolate and water in a microwave-safe bowl for about 30 seconds, stirring until melted.
4. In a small bowl, beat the egg white until stiff peaks form; set aside.
5. In another bowl, mix flour, baking soda, and salt.
6. In a large bowl, beat butter and sugar until light and fluffy. Add the egg yolk and mix well.
7. Stir in the melted chocolate and vanilla extract.
8. Alternately add the flour mixture and buttermilk, mixing until well combined.
9. Gently fold in the beaten egg white until just blended.
10. Pour the batter into the prepared pan and bake for about 20 minutes or until a toothpick comes out clean.
11. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
12. Spread coconut-pecan filling and frosting on top and enjoy!