Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large mixing bowl, beat together the softened butter, powdered sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
Add the egg and vanilla extract to the butter mixture, mixing until well combined.
In a separate bowl, whisk together the all-purpose flour, and then gradually add it to the wet ingredients. Mix until just combined.
Gently fold in the miniature semisweet chocolate chips and toffee bits until evenly distributed throughout the dough.
Using a cookie scoop, portion out the dough onto the prepared baking sheets, spacing them about 2 inches apart. Roll each scoop in additional sugar before placing them on the sheets.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. The centers may look slightly underbaked.
Allow the cookies to cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.
While the cookies are cooling, melt the chopped bittersweet chocolate in a microwave-safe bowl, heating in 30-second intervals, stirring until smooth.
Once the cookies are completely cool, drizzle the melted chocolate over the cookies using a fork or piping bag.
