2cupssemi-sweet chocolate chips or chopped chocolate(340 grams, 1 bag)
1cuppecans, finely chopped (113 grams)
Line a rimmed 13×17 sheet pan with parchment paper or a silicone baking mat.
In a heavy bottom saucepan, melt the butter over medium low heat. Stir in the sugar. Increase the heat and bring the mixture to a boil. Insert a candy thermometer and cook the mixture until it reaches 285°F, stirring occasionally.
Meanwhile, melt the chocolate in a double boiler or in the microwave in 30 second intervals, stirring occasionally.
Once the butter and sugar mixture reaches temperature, immediately pour into the lined sheet pan. Let set for a few minutes, then spread the melted chocolate on top. Immediately sprinkle with the chopped pecans.
Let set for several hours until firm, the toffee will set up quickly, the chocolate will take a while. Break the candy into small pieces. Store in an airtight container at room temperature, candy should keep for several days.