Preheat your oven to 350°F. Generously coat two standard 8×4-inch or 9×5-inch bread loaf pans with non-stick baking spray, or line them with parchment paper slings for clean extraction.

In a small bowl, stir together the 2 tablespoons of granulated sugar and 1 teaspoon of ground cinnamon until fully combined, then set this streusel mixture aside.

In an extra-large mixing bowl, combine the uncooked dry yellow cake mix and both boxes of dry instant pistachio pudding mix, whisking for 10 seconds to distribute the powders evenly.

Add the 4 large eggs, full-fat sour cream, vegetable oil, water, and green food coloring (if using) directly into the dry starch bowl.

Use an electric hand mixer on low speed for 30 seconds to moisten the ingredients, then increase the speed to medium and beat aggressively for 1 full minute until the batter is thick, velvety, and completely lump-free.

Divide exactly half of the dense green batter evenly between the two prepared loaf pans, using a spatula to smooth the layers flat. Sprinkle the cinnamon-sugar streusel mixture uniformly across the batter surfaces in both pans.

Spoon the remaining half of the pistachio batter carefully over the cinnamon layers, sealing the sugar ribbon completely inside. Drag a butter knife gently through the batter in a zig-zag pattern to slightly swirl the layers without over-blending them.

Scatter the ½ cup of finely chopped roasted pistachios evenly across the top raw surfaces of both loaves, pressing the nuts lightly into the batter so they anchor tightly during the rise.

Bake at 350°F for 40 to 45 minutes. Remove from the oven the exact moment the loaves are beautifully domed and a toothpick inserted into the center of the crumb comes out clean or with a few moist crumbs. Let the loaves cool in their pans on a wire rack for 15 minutes before transferring them to a serving plate.

While the bread cools, prepare the glaze. Whisk the sifted powdered sugar, vanilla extract, almond extract, and 2 tablespoons of whole milk together in a small bowl until smooth. Drizzle the velvety glaze generously across the warm loaves, letting it set for 10 minutes before slicing.