Melt the Butter: Carefully melt the butter in the microwave in 20-second intervals. Pour into a mixing bowl and let cool for 15–20 minutes.
Mix Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, cake flour, baking powder, cinnamon, and salt.
Cream Butter and Sugars: Add brown sugar and granulated sugar to the cooled butter. Mix for about 4 minutes, scraping down the sides.
Add Eggs and Vanilla: Beat in the egg, egg yolk, and vanilla extract. Mix well and scrape the bowl.
Add Dissolved Baking Soda: Mix the dissolved baking soda (in hot water) into the wet mixture.
Combine Dry and Wet Mixtures: Gradually add the dry ingredients to the wet mixture in 1/2 cup increments, scraping the bowl between additions.
Stir in Add-ins: Fold in the white chocolate chips, milk chocolate chips, and pecans (if using) with a wooden spoon or spatula.
Chill the Dough: Cover the dough and refrigerate for at least 3 hours (preferably overnight for better flavor).
Preheat Oven: When ready to bake, preheat the oven to 350°F (175°C). Allow dough to come to room temperature.
Scoop and Shape: Scoop the dough using a cookie scoop. Roll into balls and place on a baking sheet lined with parchment paper, leaving 2 inches between each.
Bake: Bake smaller cookies for about 10 minutes or larger cookies for 13–15 minutes, until edges are lightly golden.
Cool: Let cookies cool on the tray for a few minutes, then transfer to a wire rack to cool completely.