Preheat & Prep: Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper or grease lightly.Mix Dry Ingredients: In a medium bowl, whisk together flour, cocoa powder, baking powder, and salt.Mix Wet Ingredients: In another large bowl, combine yogurt, sugar, oil, milk, and vanilla extract. Whisk until smooth.Combine Wet & Dry Ingredients: Gradually add dry ingredients to wet ingredients, mixing gently until just combined. Fold in chocolate chips if using.Pour into Pan: Pour batter into prepared pan and smooth the top. Optionally sprinkle extra chocolate chips.Bake: Bake for 25–30 minutes. Check with a toothpick; it should come out slightly fudgy with a few crumbs.Cool & Cut: Let brownies cool in pan for 15–20 minutes, then lift out using parchment paper and cut into squares.