Here's a step-by-step guide on how to bake brownies in disposable aluminum pans:

**Ingredients:**

* 1 and 1/2 sticks of unsalted butter (12 tablespoons), plus more for greasing the pan
* 2 cups of sugar
* 4 large eggs
* 1/2 cup of unsweetened cocoa powder
* 1 teaspoon of vanilla extract
* 1 and 1/4 cups of all-purpose flour
* 1 teaspoon of salt
* 1 cup of semi-sweet chocolate chips
* Optional: nuts, espresso powder, or other mix-ins of your choice

**Equipment:**

* Disposable aluminum pans (8x8 inches or 9x9 inches)
* Mixing bowls
* Whisk
* Rubber spatula
* Measuring cups and spoons
* Oven

**Instructions:**

1. **Preheat the oven**: Preheat your oven to 350°F (180°C).
2. **Grease the pan**: Grease the disposable aluminum pan with butter or cooking spray. This will help the brownies release easily from the pan.
3. **Mix the batter**: In a large mixing bowl, combine the sugar, eggs, and vanilla extract. Whisk until well combined.
4. **Add the cocoa powder**: Add the cocoa powder to the mixing bowl and whisk until well combined.
5. **Add the flour**: Add the flour to the mixing bowl and whisk until just combined.
6. **Add the chocolate chips**: Add the chocolate chips to the mixing bowl and stir until they are evenly distributed.
7. **Pour the batter**: Pour the batter into the prepared disposable aluminum pan.
8. **Bake the brownies**: Bake the brownies for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
9. **Check the brownies**: Check the brownies frequently to prevent overcooking.
10. **Let the brownies cool**: Let the brownies cool in the pan for 10-15 minutes before removing them.
11. **Remove the brownies**: Use a spatula to carefully remove the brownies from the pan.
12. **Let the brownies cool completely**: Let the brownies cool completely on a wire rack before slicing and serving.

**Tips:**

* Use a high-quality disposable aluminum pan to ensure the brownies release easily from the pan.
* Don't overbake the brownies, as this can cause them to become dry and crumbly.
* Use a toothpick to check the brownies for doneness. If the toothpick comes out with a few moist crumbs, the brownies are done.
* Let the brownies cool completely before slicing and serving. This will help them retain their texture and flavor.

**Variations:**

* Add nuts, espresso powder, or other mix-ins to the batter for added flavor and texture.
* Use different types of chocolate chips, such as milk chocolate or white chocolate, for a different flavor profile.
* Add a layer of frosting or glaze to the brownies for an extra-special treat.