Line a 9x13” pan with foil and spray with cooking spray. You can also use parchment, if you prefer.
Melt butter in a 2-quart heavy saucepan over low heat. Stir in sugar, water, and corn syrup. Bring to a boil over medium-high heat, stirring until sugar is dissolved. Try not to splash the side of the pan too much or the sugar will stick and crystalize; stir gently.
Once sugar is dissolved, place a candy thermometer in your pan and cook over medium heat, stirring frequently, until the candy thermometer reaches 290°F (soft-crack stage). This will take from 10-14 minutes, depending on your stove. Watch the heat and adjust it as necessary to keep the boiling uniform throughout cooking. Don’t walk away from the stove; watch it especially carefully during the last 5 minutes or so as it can reach temperature fast. Remove thermometer once it gets to 290°F. Turn off heat, stir in vanilla and salt quickly. Pour into prepared pan.
Cool for 4-5 minutes just until the top is set. Sprinkle with chocolate chips. Let them sit for about 2 minutes then use a knife or offset spatula to spread the chocolate evenly. While the chocolate is sitting, place the peanut butter in a small bowl and heat about 30 seconds in the microwave to make it pourable. Drizzle peanut butter over the top and swirl with melted chocolate using a knife or offset spatula. Sprinkle with nuts.
Let sit at room temperature about 3 hours or until set. Remove toffee from pan using foil, remove the foil and then break into pieces. Store in an airtight container for up to two weeks.