Lia's Butter Toffee

*Necessary Equipment: Candy Thermometer* Combine butter, sugar, water, and salt in a saucepan. Bring to a boil, stirring constantly. Cook over moderate heat, stirring gently, until candy thermometer registers 298 degrees. Remove from heat and stir in vanilla until well combined. Pour the mixture onto a silicone baking mat or good parchment paper. Use a heatproof rubber spatula or offset spatula to spread quickly before the toffee sets. Spread thin. Allow toffee to cool completely. Blot to remove excess oil from the surface. Coat surface with half of the melted chocolate and immediately sprinkle with topping. When chocolate has totally set, carefully flip over (it's okay if it falls apart a bit) and coat other side with the rest of the chocolate. Sprinkle on topping. Allow to set, then break into bite-size pieces. Store in an airtight container.