Melt the unsalted butter in a skillet over medium heat, stirring occasionally for 5-7 minutes until it turns a lovely brown color and develops a nutty aroma.

In a large bowl, combine the brown butter, brown sugar, and granulated sugar. Mix until fluffy.

Add the egg, vanilla extract, and brewed coffee, and stir until well-blended.

In a separate bowl, whisk together the flour, baking soda, and salt.

Gradually fold the dry mixture into the wet ingredients until well combined.

Stir in the toffee bits gently.

Scoop tablespoons of cookie dough onto a lined baking sheet, spacing them out to allow for spreading. Optionally, sprinkle with flaky sea salt.

Bake in a preheated oven at 350°F (175°C) for 10-12 minutes or until the edges are golden brown.

Let cookies cool on the baking sheet for a few minutes before transferring to a wire rack.