Creating the Best Raspberry Swirl Brownies is a straightforward process. Follow these steps to achieve delicious results:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking pan.
2. Prepare the Raspberry Swirl: In a small bowl, combine the raspberries, 2 tablespoons of sugar, and lemon juice (if using). Mash gently with a fork until slightly pureed. Set aside.
3. Melt the Butter: In a medium saucepan, melt the butter over low heat. Remove from heat and let it cool slightly.
4. Mix the Brownie Batter: In a large mixing bowl, combine melted butter and granulated sugar. Stir until well blended.
5. Add Eggs and Vanilla: Add eggs one at a time, mixing well after each addition. Then stir in the vanilla extract.
6. Combine Dry Ingredients: In another bowl, whisk together the flour, cocoa powder, salt, and baking powder.
7. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until fully combined and smooth.
8. Pour into Pan: Pour the brownie batter into the prepared baking pan, spreading it evenly.
9. Add Raspberry Swirl: Spoon dollops of the raspberry mixture over the brownie batter. Use a knife or toothpick to swirl the raspberry into the batter gently.
10. Bake: Place the pan in the preheated oven and bake for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
11. Cool: Remove from the oven and allow the brownies to cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely.
12. Cut and Serve: Once cooled, cut the brownies into squares and serve.

Following these steps will guide you in creating these incredible brownies with ease and confidence.