Add butter to a small sauce pan, melt and bring to a boil over medium-high heat. Reduce to medium heat and continue to cook 4-5 minutes until butter is golden in color. While butter is browning, add coconut flakes to a small pan and stir over medium-high heat for 3-4 minutes until browned (but careful not to let them burn!).
Add butter, brown sugar, vanilla, and eggs to a large bowl and mix until smooth. In another bowl whisk together flour, baking powder, oats, toasted coconut flakes, and 1/2 teaspoon salt.
Add dry ingredients to wet ingredients and mix until combined. Mix in milk. Stir in chocolate chips and macadamia nuts. Spread mixture into the bottom of a greased 9x13 inch baking pan. (If desired, sprinkle coarse sea salt on top - I used about 1 teaspoon).
Bake at 350 for 20-25 minutes until golden brown on top. Allow to cool completely before cutting into bars. Store in airtight container.