Preheat your oven to 350°F (175°C). Line your baking sheets with parchment paper to prevent sticking.
In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and table salt. Set this mixture aside.
In a large mixing bowl, use an electric mixer to cream together the softened unsalted butter, light-brown sugar, and granulated sugar until the mixture is light and fluffy.
Beat in the eggs, one at a time, ensuring each is fully incorporated before adding the next. Mix in the vanilla extract until well combined.
Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix!
Gently fold in the chopped bittersweet, semi-sweet, and milk chocolate chunks, along with the chopped Fishers Walnuts, using a spatula.
Using a cookie scoop, portion out the dough onto the prepared baking sheets, spacing them about 2 inches apart.
If desired, sprinkle a few Maldon sea salt flakes on top of each cookie dough ball for an added touch of flavor.
Bake the cookies in the preheated oven for 10 to 12 minutes, or until the edges are golden and the centers look slightly underbaked. They will continue to cook on the baking sheet after being removed from the oven.
Let the cookies cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.
