Cover sheet with 40 Saltine crackers. Spread shredded coconut in a single layer on top of crackers. Add butter and sugar to a heavy-bottomed pot. Attach a candy thermometer to the pot.
Bring to a simmer over medium-low heat, stirring frequently to dissolve sugar. Increase heat to medium-high. Once the candy starts boiling, stir occasionally, slowly and evenly, until candy reaches 290 F. This is the "hard crack" stage on a candy thermometer.
Bake in preheated oven for 4-5 minutes. Remove from oven and add chocolate chips. Use a spatula to spread the chocolate evenly once the chips begin melting. Add remainder of the coconut flakes, sprinkling evenly over the top of the chocolate.