Preheat your oven to 350°F (177°C). Line an 8x8-inch pan with parchment, leaving overhang for easy lifting.
Make the brownie batter: Melt butter in a saucepan or microwave-safe bowl. Whisk in sugar, then add eggs and vanilla until glossy.
Sift cocoa powder, flour, salt, and baking powder.
Stir into the wet mixture just until combined. Do not overmix.
Spread batter evenly into the prepared pan. Bake for 20–24 minutes, until a toothpick comes out with moist crumbs. Cool completely in the pan.
Prepare strawberries: Toss diced berries with sugar and lemon juice.
Let sit 10–15 minutes to macerate and release juices.
Make the cream topping: Beat heavy cream, powdered sugar, and vanilla to soft peaks. If using cream cheese, beat it separately until smooth, then fold or beat into the whipped cream until thick and spreadable.
Assemble: Pat strawberries lightly with a paper towel to remove excess moisture. Spread the cream topping over cooled brownies.
Spoon strawberries evenly on top.
Chill for 30–60 minutes to set the topping. Lift from the pan and slice with a sharp knife, wiping between cuts for clean squares.