• Preheat oven to 350F (177C) and line cookie sheets with parchment paper.  Set aside.
• Cut your butter into Tablespoon-sized pieces and place in a medium-sized saucepan. Melt over medium-low heat.
  
  1 cup unsalted butter

To Brown the Butter (It's easy, I promise!)

• Once butter has melted, increase heat to just above medium heat.
  
• Swirl and scrape the sides of the pan frequently with a wooden spoon or heatproof spatula - the butter will bubble and pop. Once the bubbling/popping slows, the butter will begin to turn brown, it will look like this once it's finished: 
  
• Watch the butter very carefully at this point, and once it begins to brown and you smell the nutty aroma of browned butter, remove from heat quickly and pour into a large, heatproof bowl.  
• Allow butter to cool for 25-30 minutes before proceeding with the recipe.

Cookie Dough

• Add sugars into cooled browned butter, stir well.
  1 cup brown sugar, ⅔ cup white sugar
• Stir in eggs, one at a time, stirring well after each addition.
  2 eggs
• Add vanilla extract and stir.
  1 ½ teaspoon vanilla extract
• In a separate, medium-sized bowl, whisk together flour, cornstarch, baking powder, baking soda and salt.
  2 ¾ cups all-purpose flour, 1 teaspoon cornstarch, 1 teaspoon baking powder, 1 teaspoon baking soda, ¾ teaspoon salt
• Gradually add flour mixture to butter mixture, stirring until ingredients are nearly completely combined.
• Add milk chocolate toffee bits and stir until ingredients are well-incorporated.
  1 cup milk chocolate toffee pieces
• Drop by heaping, rounded 1 ½ Tbsp (45g) scoops onto prepared cookie sheets, placing at least 2" apart.
• Bake on 350F (177C) for 9-10 minutes or until edges are just beginning to turn golden brown (cookies should still be quite soft when you remove them from the oven, and may even appear slightly underbaked in center).
• Sprinkle lightly with sea salt.
  sea salt
• Allow cookies to cool on baking pan for about 3 minutes and then use a spatula to gently scoop beneath them and carefully wiggle them free from the parchment paper, as the toffee tends to stick.  
  
• Allow to cool several more minutes and then transfer to cooling rack to cool completely.