1. **Preheat:** Preheat your oven to 350°F (175°C). Line an 8×8-inch square baking pan with parchment paper, leaving an overhang on the sides for easy removal.

2. **Mix Butter & Sugar:** In a medium microwave-safe bowl, melt the butter. Add the vegetable oil and sugar to the hot butter. Whisk vigorously by hand for about a minute. (Whisking while the butter is hot helps dissolve the sugar, which creates that shiny crackly crust).

3. **Add Wet Ingredients:** Whisk in the eggs and vanilla extract. Beat for another minute until the batter is pale and slightly slightly thickened.

4. **Add Dry Ingredients:** Sift the flour, cocoa powder, and salt into the bowl. (Sifting is important to remove cocoa lumps).

5. **Fold:** Switch to a spatula and gently fold the dry ingredients into the wet ingredients just until no flour streaks remain. Do not overmix, or the brownies will be tough.

6. Fold in the chocolate chips if using.

7. **Bake:** Pour the batter into the prepared pan and smooth the top. Bake for 20–25 minutes. A toothpick inserted into the center should come out with moist crumbs attached (not wet batter). If it comes out clean, they are overbaked!

8. **Cool:** Let the brownies cool completely in the pan before lifting them out using the parchment paper. Slicing them while hot will cause them to fall apart.