Heavily line a half sheet pan with foil and arrange the crackers side-by-side in an even layer.
In a heavy bottom 2-quart saucepan, add the butter and brown sugar. Bring to a boil over medium-high heat, stirring occasionally, until the mixture comes to a boil.
Once the sugar has dissolved, pour the toffee over the crackers, and then use a spatula to smooth it out over the entire surface.
Bake in a preheated oven for 5 minutes.
Remove and immediately sprinkle with the milk chocolate chips. Once the chocolate chips have begun to soften, use an off-set spatula to spread the melted chocolate evenly over the toffee.
Serve as is or sprinkle with flaky salt, nuts, sprinkle or candy of choice.
Once the pan has cooled, place it in the fridge until the toffee and chocolate are set, about 30 minutes. Break it up into any size pieces you'd like and serve. The toffee can be stored in an airtight container for up to one week.