Preheat oven to 350 degrees F. Line a 9x13 pan with parchment and set aside.
PREPARE THE CRUST
In a large bowl, combine the egg, butter and sugar. Mix until creamy. Add flour and salt and stir until combined. Using your fingers (flour them, if needed), press the dough evenly into the bottom of the prepared pan. Bake in the preheated oven for 15 minutes.
PREPARE THE FILLING
Spread chocolate chips evenly over crust (if using). In a medium bowl, combine berries, sugar and lemon juice. Stir until combined. Pour evenly over crust/chocolate chips.
PREPARE THE TOPPING
In a small bowl, combine the brown sugar, flour and butter. Stir until mixture is crumbly. Spread evenly over filling layer. Bake for an additional 30-40 minutes. Let cool and cut into squares.
Notes
Chocolate chips can be omitted completely for a berry-focused dessert.
Any combination of raspberries, blackberries, blueberries or chopped strawberries can be used.
Let both butter and egg sit at room temperature for 30 minutes if at all possible.