Cover the sheet with 40 Saltine crackers. Spread the shredded coconut in a single layer on top of the saltine crackers. Add butter and sugar to a heavy-bottomed pot, at least 2 quarts in size. Attach a candy thermometer to the pot.
Bring to a simmer over medium-low heat, stirring frequently to dissolve the sugar. Increase heat to medium-high. Once the candy starts boiling, stir occasionally, slowly and evenly, until the candy reaches 290 F to 300 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, sprinkling evenly across the toffee. 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.