Place the melted butter, 1 cup flour, and ¼ cup powdered sugar in a large bowl. Stir until just combined.
Pat into a 9x12 inch pan (a 9x13 inch pan works, too). Bake in the preheated oven for 12–15 minutes, or until just golden brown.
Meanwhile, place the remaining ingredients in the same large bowl. Stir just until combined.
Spread the mixture over the partially baked crust, and return to the oven. Bake for 18–20 minutes, or until golden all over the top. Remove from the oven and allow to cool for 20 minutes.
Cut into squares while still slightly warm.
Notes
These make a thin bar cookie. Both the crust and the filling should be spread in an even layer to cover the pan. I've made these with both sweetened and unsweetened coconut, and didn't notice much of a difference. Make them with whichever shredded coconut that you have on hand! Coconut bars will keep in an airtight container at room temperature for up to one week. You can also freeze them for up to 3 months.