Preheat oven to 350 degrees F. Spray 8x8-inch pan with nonstick spray and then line the bottom with parchment paper.
Heat butter in a small saucepan over medium heat until it browns and begins to smell nutty (watch it closely so it doesn't burn). Let the butter cool for a few minutes, until just barely warm.
In a large mixing bowl, combine the browned butter and sugars. With a wooden spoon, stir in egg, vanilla and salt. Stir in flour, coconut and M&Ms until batter is blended.
Pour the batter into the prepared pan and smooth the top with a rubber spatula. Sprinkle a few additional M&M's on top. Bake 25 to 30 minutes. Let the blondies cool before turning them out onto a cutting board and slicing into squares (chilling them will make that process even easier).
Notes
*Use chocolate chips in place of M&Ms if you'd like.*For slightly gooey, under baked blondies, bake for 25 minutes. For fully baked blondies, bake the entire 30 minutes (I baked mine for about 27 minutes and I thought that they were perfect!).