Preheat oven to 350ºF. Line a 10x15” pan (jelly roll or cookie sheet with sides) with foil and spray well with cooking spray. Lay the graham crackers in a single layer in the pan, breaking a few to fill in the edges and gaps as much as possible.

Melt butter in a saucepan over medium heat. Turn to medium-low and add brown sugar and water. Bring to a boil, stirring occasionally. Once it boils, place the candy thermometer in the pan and do not stir. Let the mixture cook until it reaches 255ºF on a candy thermometer, about 5-7 minutes. Remove from the heat and stir in vanilla extract. Immediately pour over cookies and spread carefully to cover all the crackers. Bake for 5 minutes.

Remove the pan from the oven and sprinkle with the chocolate chips. Bake an additional 2 minutes. Remove the pan from the oven and, using an offset spatula, carefully spread the chocolate chips evenly over the toffee (they will have melted in the oven but still held their shape). Sprinkle your Halloween sprinkles and/or candies over the chocolate. Let cool to room temperature, then chill to set. Break into pieces and serve.