Preheat the oven to 400°F.
Line a 10x15-inch pan with aluminum foil and lightly grease.
Place the saltine crackers on the cookie sheet to cover the entire pan in 1 layer of crackers.
Melt the butter and sugar in a medium saucepan over medium heat.
Once the butter is melted, bring it to a boil for 3 minutes while stirring constantly. The brown sugar mixture must boil for exactly 3 minutes. If it doesn't boil long enough the mixture won’t set and will make the crackers soggy.
While stirring the mixture, consistently scrape the sides otherwise the sugar will crystallize on the sides of the pan.
Carefully pour the mixture over the crackers. Spread it overtop so that all of the crackers are covered.
Bake in the oven for 5 minutes. Remove from the oven and cool for 5 minutes.
Add the chocolate to a medium heatproof bowl. Microwave on medium power for 1-minute bursts, stirring between each. When the chocolate is almost melted, stir until smooth.
Spoon the chocolate over the crackers, and spread it smooth completely coverving the pan. Decorate with sprinkles.
Let the toffee harden until the chocolate is set at room temperature or in the fridge.
Once completely hardened, remove from the pan and peel the aluminum foil off. Break/"crack" it into pieces.