Grate the yellow squash and zucchini using a box grater or food processor, then place each in a clean kitchen towel and squeeze firmly to remove excess moisture—this is crucial for preventing a soggy loaf. While squeezing, preheat your oven to 350°F and lightly grease a 9x5 inch loaf pan or similar size with butter or non-stick spray.

In a small bowl, whisk together the flour, baking powder, baking soda, salt, allspice, cinnamon, and nutmeg. I like to sift these together rather than just whisking because it breaks up any lumps in the baking soda and distributes the spices evenly throughout—this ensures every bite has consistent flavor.

In a large bowl, whisk together the melted and cooled butter, eggs, both sugars, and vanilla until well combined and slightly lighter in color. Make sure the butter is cooled before adding eggs to avoid scrambling them. Add the squeezed-dry squash and zucchini from Step 1 and stir until evenly distributed throughout the wet mixture.

Fold the dry ingredient mixture from Step 2 into the wet mixture from Step 3 using a spatula or wooden spoon, stirring just until combined—do not overmix, as this can develop gluten and make the bread tough. Fold in the 1/2 cup roughly chopped nuts, then pour the batter into your prepared loaf pan. I recommend tapping the pan gently on the counter a few times to release any large air pockets before topping.

In a small bowl, combine the 1/4 cup nuts, 1 tsp cinnamon, and 1 tbsp sugar to create a cinnamon-nut topping. Sprinkle this mixture evenly over the batter in the pan. Bake in the preheated 350°F oven for 45-50 minutes, until a toothpick inserted into the center comes out clean or with just a few moist crumbs.

Remove the bread from the oven and let it cool in the pan for 10 minutes. This resting time allows the crumb structure to set so it won't fall apart when you remove it. Turn the loaf out onto a wire rack to cool completely before slicing.