Preheat oven to 350'F. Grease an 20 cm square baking pan. Combine the butter and brown sugar in a sturdy saucepan and set over moderate heat. Stir frequently until the mixture is bubbly and the sugar is melted, then set aside to cool slightly. Beat the eggs and vanilla into the butter and brown sugar mixture. Combine the flour, baking powder and salt, then stir and toss them together. Add to the first mixture and beat just until thoroughly mixed. Stir in the pecans and the coconut. Spread the batter evenly in the prepared pan. Bake for about 30 minutes, or until the top is dry and a toothpick inserted in the center of the brownies comes out barely clean. Remove from oven and cool on a rack. Cut into 5 cm squares.