Penuche I

Combine white sugar, light brown sugar, heavy cream, and molasses in a heavy-bottomed saucepan over medium heat, stirring until the sugars dissolve completely.

Add unsweetened chocolate and butter to the mixture, stirring constantly until both are fully melted and incorporated.

Stop stirring once the mixture comes together and insert a candy thermometer, monitoring the temperature as it rises.

Continue cooking without stirring until the mixture reaches 238°F (soft-ball stage), approximately 10–12 minutes.

Remove from heat immediately and allow the mixture to cool to approximately 110°F, about 5–10 minutes, without stirring.

Stir in vanilla extract and chopped nuts (if using) vigorously with a wooden spoon or spatula until the mixture loses its shine and becomes thick and creamy, roughly 3–5 minutes.

Pour the penuche into a buttered 8×8-inch pan, spreading it evenly with a spatula.

Allow to cool completely at room temperature, then cut into squares and serve.