Start by lining a 11"x17" sheet pan with parchment paper. I prefer to just use parchment because I feel like greasing the pans adds that layer to the finished toffee. It is important to you do this step first, in order to ensure a smooth process.
Over medium heat melt 3 sticks of butter in a medium saucepan over medium heat.
Once butter melts add water and sugar to the center of the pot, this prevents the sugar from crystallizing on the side of the pan.
Next, embrace your inner Gaston and stir vigorously for the next 10 or so minutes, you are going to want to use a wooden spoon so your spoon doesn't melt. Once your mixture starts to darken, insert your candy thermometer and bring the mixture to 300° or the hard crack stage. If you don't have a thermometer get the mixture to the color of peanut butter and quickly test by dropping some of the mixture in ice water for 10 seconds. If you pull it out and it crunchy and cracks you are good to go.
Pour the toffee mixture onto your prepared baking sheet and quickly spread out with a spatula. If it doesn't fully cover the pan that is okay, just try to keep it as square as possible if you are looking to make yours look like the Disneyland version.
If you are going for the Disneyland look, after 5 minutes of cooling use a knife to cut the toffee into large rectangles. It might take a few passes to get all the way through the toffee.
Let the mixture cool for at least 1-2 hours or until nicely set.