Arrange a rack in the middle of the oven and heat to 325°F. Butter or spray a 24-well mini-muffin tin.
Stir the pecans, chocolate, and coconut together in a medium bowl; set aside.
Place the butter, brown sugar, granulated sugar, and salt in a stand mixer fitted with the paddle attachment and beat on medium speed until smooth, about 3 minutes. (Alternatively, use a large bowl and electric hand mixer.) Add the egg and beat on low, scraping the bowl as needed, until you have a smooth, creamy mixture. Beat in the vanilla.
Turn the mixer off, add the flour all at once, and pulse a few times to start incorporating it. Mix on low speed until the flour is almost fully blended into the dough. Add the pecan mixture, mixing just until they're evenly distributed; if you'd like, you can do the last few turns by hand with a sturdy rubber spatula.
Using a small cookie scoop, scoop out level portions of dough or use a teaspoon to make rounded spoonfuls and place one in each mini-muffin well. When each well has dough (you will use about half the dough), press each mound of dough down very lightly with moistened fingertips.
Bake until the cookies are firmly set around the edges and golden-brown in the center, 14 to 16 minutes. A tester inserted in the center of a blondie should come out clean.
Place the tin on a cooling rack and let the blondies rest for 3 minutes. Unmold the blondies either by turning the tin over and rapping them against the counter or popping the blondies out with table knife. Transfer the blondies to the rack and and let cool to room temperature, about 10 minutes.
Let the mini-muffin tin cool and and repeat baking the remaining dough.
Recipe Notes
Make ahead: You can scoop the dough out onto a lined baking sheet, pat it down, freeze until firm, and then pack the pucks in an airtight container and freeze for up to 2 months. Leave the pucks at room temperature while you heat the oven before baking.
Storage: The blondies are best eaten soon after they're baked, but they can be kept in a covered container at room temperature for up to 1 day. They can also be frozen, wrapped airtight, for up to 2 months.
