Preheat the oven according to the brownie mix directions. (I prefer 325°F / 165°C for a more even bake.) In a medium bowl, combine the water, egg, and oil or softened butter—whatever your mix calls for. Mix until the egg is fully incorporated. (Tip: I like using softened butter instead of oil. It doesn’t fully blend at first, but once combined with the mix, it creates a fluffier, cakier texture.)
1 box brownie mix (my preferred brand) + ingredients for that mix (water, oil, egg etc.)
Add the wet mixture to the brownie mix in a large bowl. Stir with a wooden spoon until fully combined.
Spread the batter evenly into a 9-inch (23 cm) tart pan with a removable bottom. Bake according to the package directions, usually about 39 to 43 minutes, until the center is set and the edges start to pull away from the pan.
Remove from the oven and let the brownie cool completely before removing it from the pan.
In a medium bowl, beat together the softened cream cheese, confectioners’ sugar, heavy cream, and vanilla extract until smooth and fluffy. (Add an extra tablespoon [15 mL] of cream if you want a softer texture.)
1 package (8 oz 226 g) cream cheese, softened, ⅓ cup (40 g) confectioners' sugar, 2 tbsps. (30 ml) heavy whipping cream, ½ tsp (2.5 ml) vanilla extract
Transfer the cooled brownie base to a serving tray. Spread the cream cheese frosting evenly over the top.
Arrange the sliced strawberries, blueberries, and raspberries over the frosting.
1½ cups (225 g) fresh strawberries, sliced, 1 cup (125 g) fresh raspberries, 1 cup (150 g) fresh blueberries
Chill for at least 1 hour before slicing.
Cut into wedges and serve. Store leftovers in the refrigerator.