Preheat oven to a 350°F. Grease a 9 x 13-inch baking pan to ensure nothing sticks. Scatter walnuts on a cookie sheet and toast them in the oven for 5 to 7 minutes, or until they've turned a shade of golden brown, filling the air with a nutty aroma.

In a mixing bowl, whisk together the brown rice flour, potato starch, tapioca starch, baking powder, xanthan gum, and a dash of salt. Stir until well combined, creating a foundation of flavors and textures.

In a separate bowl, start the alchemy of butter and light brown sugar. Beat them together on low speed until just combined, then escalate to high speed, whipping the mixture into a light and fluffy cloud for 3 to 4 minutes. Introduce the eggs, one at a time, along with the vanilla extract, and beat for another minute, weaving in richness and depth.

Slowly merge the dry ingredients with the buttery mixture, beating until they are fully united. Softly fold in the toasted walnuts and the tart chopped cranberries, creating a dough that's rich with contrasts. With care, spread the dough evenly in your greased pan, smoothing it into the corners.

Place the pan in the oven and bake for 20 to 25 minutes, or until the top has turned a delightful shade of brown and the aroma of baking bliss fills the kitchen. Let the squares to cool completely in the pan, set on a cooling rack. Once cooled, cut into squares, each a perfect piece of your baking journey.

A Delightful Twist: For a different twist, switch out the walnuts for chopped almonds and replace the vanilla extract with almond extract, offering a new melody of flavors to explore.