Preheat oven to 350F. Line an 8-by-8-inch pan with aluminum foil, spray with cooking spray; set aside.
In a medium microwave-safe bowl, melt the butter, about 60 seconds. To the melted butter, add the brown sugar and stir to combine. Add the egg, vanilla, and stir to combine. Add the flour, salt, and stir until just combined, taking care not to over-mix or the blondies will be tough. Fold in the coconut. Fold in white chocolate chips and pour batter into prepared pan, smoothing it lightly with a spatula or offset knife if necessary.
Bake for 23 to 27 minutes, or until edges begin to slightly pull away from sides of pan, center is set and golden, and a toothpick comes out clean; do not overbake. Note: if blondies appear to be browning too fast on top, you may wish to lower your oven temperature to 325F midway through cooking; both coconut and white chocolate have a tendency to cook quickly and burn easily. Allow blondies to cool for at least 45 minutes before drizzling with melted chocolate.
In a medium microwave-safe bowl, melt the chocolate chips on high powder, about 1 minute, or until they can be stirred smooth. Drizzle blondies with melted chocolate using a spoon. Allow chocolate to set before slicing and serving, at least 15 minutes. Blondies can be stored in an airtight container at room temperature or in the refrigerator for up to 1 week, or in the freezer for up to 3 months.
The blondies are ripe for substitutions and variations. Add or Try: Other baking chips; butterscotch chips, peanut butter chips, milk chocolate chips; toffee bits, fresh or frozen fruit including cherries, peaches, nectarines, blackberries, raspberries, blueberries; macadamia nuts or slivered almonds; diced candy such as Snickers, Butterfingers, M&Ms, Reese’s Pieces or whatever strikes your fancy. To keep gluten-free, use your favorite gluten-free flour blend.