Line a 9x13-inch pan with parchment paper; set aside.
In a heavy saucepan, add butter, sugars, and salt. Cook over medium-low heat, stirring constantly, until it boils.
Stop stirring and let the mixture boil until it reaches 290–300°F on a candy thermometer (hard crack stage).
Remove from heat and stir in vanilla extract. Pour into the prepared pan and let sit for 5 minutes.
Sprinkle chocolate chips over the toffee. Let them soften, then spread smooth with a spatula.
Add nuts, sea salt, or sprinkles, if desired.
Cool completely in the fridge, then break into pieces.