Preheat oven to 350. Butter and flour a 13 x 9 inch baking pan.
Melt butter in a 3-qt heavy saucepan over low heat, stirring, until smooth. Remove from heat and cool to lukewarm. Whisk in brown sugar and vanilla. Whisk in eggs 1 at a time until mixture is glossy and smooth.
Whisk together flour, baking soda, and salt, then whisk into butter mixture. Stir in pecans and 1 1/2 cups coconut.
Spread in pan and sprinkle with remaining coconut. Bake about 35 minutes. Cool completely.