Swirling Technique: For a stunning marbled effect, gently warm the blackberry preserves before drizzling them over the cheesecake layer. Use a knife to carefully swirl the preserves, making sure both the cheesecake and brownie layers remain clearly visible.

Ingredient Quality: The flavor and texture of your brownies will be significantly enhanced by using high-quality cocoa powder and fresh blackberries (if you're using them as a garnish). If possible, choose organic or artisanal preserves for an even richer taste.

Serving Suggestions: These brownies are delicious on their own, but for an extra indulgent treat, pair them with a scoop of vanilla ice cream or a dollop of whipped cream. A light dusting of powdered sugar or a few fresh blackberries on top will also add a delightful finishing touch.

Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper or lightly grease it.

In a medium mixing bowl, combine the melted butter, 1 cup of sugar, eggs, and 1 teaspoon of vanilla extract. Stir until everything is well blended.

Add the cocoa powder, flour, salt, and baking powder to the wet mixture. Stir until just combined, being careful not to overmix.

Pour the brownie batter into the prepared pan, spreading it evenly.

In another mixing bowl, beat the cream cheese, 1/4 cup of sugar, egg, and 1/2 teaspoon of vanilla extract until smooth and creamy.

Spoon the cheesecake mixture over the brownie batter in dollops, then use a butter knife to gently swirl the two together.

Warm the blackberry preserves slightly in the microwave, then drizzle it over the cheesecake layer. Use the knife to swirl the preserves into the batter, creating a marbled effect.

Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs. Allow the brownies to cool in the pan before cutting them into squares.

Garnish with fresh blackberries if desired.