Preheat your oven: Set your oven to 375°F (190°C) and lightly grease a medium baking dish (10.5 x 7.5 inches) with cooking spray or a thin layer of olive oil.
Sauté scallions: In a large frying pan, heat 1 teaspoon of olive oil over medium heat. Add the diced scallions and sauté for about 1-2 minutes until they become soft.
Add spinach: Toss in half of the 10 oz of rough chopped baby spinach to the pan and stir until it wilts, about 2 minutes. Transfer to a bowl, drain any excess moisture and pat dry.
Repeat with remaining spinach: Add another teaspoon of olive oil to the pan and repeat the process with the remaining spinach until all of it is wilted and dried.
Mix dry ingredients: In a separate bowl, whisk together 1 cup of all-purpose flour, 1 teaspoon of baking powder, and 1 teaspoon of salt until well combined.
Combine wet ingredients: To the same bowl, add the 1 cup of milk, 2 lightly beaten eggs, and 1/4 cup of melted butter (or olive oil). Mix well until smooth.
Fold in the flavor: Carefully fold in the sautéed spinach, chopped dill, 4 oz of shredded mozzarella, and 4 oz of crumbled feta until evenly distributed throughout the batter.
Pour and bake: Pour the mixture into the prepared baking dish. Sprinkle the top with 2 tablespoons of grated Parmesan cheese to create a delicious crust. Bake in the preheated oven for 40 to 45 minutes, or until golden brown.
Cool and serve: Once baked, remove from the oven and allow the brownies to cool for about 15 minutes before slicing into squares.
Each step of the process is simple and straightforward, ensuring that even novice cooks can create impressive results. Pay attention to the texture; the batter should be thick but pourable, and the baked brownies should be set with a slight spring when touched.