A candy surprise makes this snack a best seller. Fun to make and easy to package, bake sale bars have long been a favorite of fund-raising parents. Our bar, made with unsweetened coconut and toasted pecans (an ingredient kids will have fun crushing up), packs a lot of taste, but it gets its surprise crunch from crushed Heath bars. A word of advice: once you've sampled the batch, wrap the rest quickly, or you may see your profits disappear.
Heat the oven to 350º. Grease the bottom and sides of a light-colored 13- by 9-inch baking pan, then lightly flour it, knocking out the excess. Set the pan aside.
On a separate baking sheet, spread the pecan halves and toast them in the oven for 7 minutes. Once they're cool to the touch, set the pan on a solid work surface and use a saucepan to finely crush the pecans. Then transfer them to a medium-size bowl.
Toast the coconut in a nonstick skillet over medium heat, stirring with a wooden spoon, until the coconut is light golden in color, about 10 minutes. Transfer the coconut to the bowl with the pecans.
Seal the Heath bars in a heavy-duty gallon-size plastic bag, then crush them with a rolling pin. Transfer the bits to the bowl with the pecans and coconut, breaking up any larger pieces by hand.
Melt the butter, pour it into a large bowl, and let it cool to lukewarm. Using a wire whisk, blend in the sugars until they're smooth. Whisk in the eggs, milk, and vanilla extract.
Using a wooden spoon, combine the flour, cornstarch, baking powder, and salt in a medium bowl. Add the dry ingredients to the butter mixture, stirring until they are evenly blended, then stir in the pecans, coconut, and Heath bar bits.
Use the back of a large spoon to evenly spread the dough in the prepared baking pan. Bake the bars on the center oven rack until the top is a light, golden brown and the edges are crackly, about 25 minutes. Transfer the pan to a wire rack and cool thoroughly, about 1-1/2 hours, before slicing. Makes 24 bars.