Preheat your oven to 375F (190C).
Line a sheet tray with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, baking powder, and salt. Set aside.
In a large bowl, using an electric mixer, beat butter, peanut butter, and sugars until light and fluffy.
*You can also do this by hand.
Mix in the whole egg, and then add the vanilla extract.
Gradually mix in the dry flour mixture until fully incorporated.
*Try to avoid over-stirring the mixture here once you have added the dry ingredients.
Gently stir in the chocolate chips and chopped walnuts.
Refrigerate the dough for at least 45 minutes.
*This refrigeration step makes a big difference!
Drop the cookie dough using a large spoon in heaping tablespoons onto the parchment paper on a baking sheet, spaced about 3 inches apart.
Use your fingers to press down into the center of each cookie dough ball, leaving the sides of the cookie dough higher than the center portion.
Drop a teaspoon of dulce de leche and a teaspoon of peanut butter into the center of each cookie dough ball.
Top the dulce de leche and peanut butter with some of the finely-crushed almonds.
Create another cookie dough ball, and press it into a disk.
*This will serve as the “lid” for your stuffed cookie.
Place the cookie dough disk on top of the filled cookie dough base you created earlier, and gently press to seal the edges.
Sprinkle a few pieces of Maldon Sea Salt on the top of each cookie before baking.
Bake the cookies at roughly 375F (190C) for about 12-14 minutes, or until cookies have baked through and are golden brown in color.
Allow the cookies to cool at room temperature for 10 minutes before serving.