In a medium saucepan over medium heat, melt the butter while stirring continuously until it reaches a deep amber color, about 5-7 minutes.

In a large mixing bowl, combine the warm brown butter with both granulated and brown sugars, blend until light and fluffy, about 2-3 minutes.

Whisk together Irish rolled oats, all-purpose flour, baking soda, and a pinch of salt in a separate bowl.

Gradually incorporate the dry mixture into the wet ingredients, stirring gently until just combined.

Cover the bowl with plastic wrap and refrigerate the cookie dough for about 30 minutes.

Preheat your oven to 350°F (175°C) while the dough chills.

Scoop tablespoon-sized portions onto a baking sheet, flatten slightly, and sprinkle with flaky sea salt if desired.

Bake in the preheated oven for 10-12 minutes until edges are golden, and centers appear underbaked.

Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.