Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.

In a medium saucepan, combine butter, sugar, water, and corn syrup. Cook over medium heat, stirring constantly, until mixture reaches 300°F (150°C) on a candy thermometer.

Immediately pour the hot toffee mixture onto the prepared baking sheet, spreading it evenly with a spatula.

Sprinkle semisweet chocolate chips evenly over the hot toffee and let sit for 2 minutes to soften.

Spread the melted chocolate into an even layer with an offset spatula.

Melt white, pink, and red candy melts separately and drizzle over the chocolate layer.

Immediately add Valentine sprinkles while the chocolate is still wet.

Let cool completely at room temperature or refrigerate for 30 minutes until set.

Break into pieces and store in an airtight container.