Preheat oven to 350°F (175°C).

Melt 13 ounces semi-sweet chocolate and butter together in a double boiler or microwave.

Remove from heat and let cool slightly.

In a mixing bowl, cream together 8 ounces cream cheese, 1 3/4 cups sugar, and eggs.

Beat until well mixed and smooth.

Add vanilla, flour, baking powder, and salt to the cream cheese mixture.

Slowly incorporate the melted chocolate mixture into the cream cheese mixture until smooth.

Pour the brownie batter into a greased 9x12 inch baking pan.

In a separate bowl, beat 3 ounces cream cheese, lemon juice, and 1/4 cup sugar until creamy and smooth.

Continue beating while adding eggs one at a time, ensuring each egg is fully incorporated.

Pour the lemon mousse mixture evenly over the brownie batter in the pan.

Place 6 ounces semi-sweet chocolate and whipping cream in a double boiler or microwave.

Heat until the chocolate melts and the mixture is smooth.

Stir the ganache until well combined.

Drizzle the melted chocolate ganache over the lemon mousse layer.

Bake in the preheated oven for approximately 45 minutes, or until a toothpick inserted into the center comes out with moist crumbs.

Remove from the oven and let cool completely.

Chill in the refrigerator before cutting into squares and serving.