Step 1: Lightly grease a 9×13-inch baking dish. In a medium bowl, combine 2 cups of finely crushed graham cracker crumbs with 1/2 cup of melted unsalted butter and 1/4 cup of granulated sugar. Mix until the crumbs are evenly moistened.
Step 2: Press the crumb mixture firmly and evenly into the bottom of the prepared baking dish. Use the bottom of a glass or a flat measuring cup to compact it tightly. Place the crust in the freezer for at least 15 minutes to firm up while you prepare the filling.
Step 3: In a large mixing bowl, beat 8 ounces of softened full-fat cream cheese with 1/2 cup of powdered sugar and 1 teaspoon of vanilla extract until light and fluffy, about 2-3 minutes. Make sure there are no lumps.
Step 4: In a separate, very cold bowl, whip 1 ½ cups of cold heavy cream until stiff peaks form. Gently fold the whipped cream into the cream cheese mixture in three additions, being careful not to deflate the cream. The goal is a light and airy velvet cream.
Step 5: Spread the cream cheese mixture evenly over the chilled graham cracker crust. Smooth the top with an offset spatula or the back of a spoon. Cover the dish loosely with plastic wrap.
Step 6: Refrigerate the slice for at least 4-6 hours, or preferably overnight, to allow the filling to set completely and the flavors to meld. Chilling is crucial for clean slices.
Step 7: Before serving, gently wash and pat dry 1 cup of fresh strawberries (hulled and sliced), 1 cup of fresh raspberries, and 1 cup of fresh blueberries. Arrange the fresh berries decoratively over the set cream layer. Slice and serve immediately.