Brownie Cake:

1. Preheat the oven to 350°F (175°C).
2. Grease three 8-inch round baking pans with cooking spray and line the bottoms with parchment paper.
3. In a large bowl, combine the sugar and vegetable oil. Mix with a wooden spoon until fully incorporated.
4. Add the eggs one at a time, stirring and allowing each egg to blend in before adding the next.
5. Stir in the vanilla extract until well mixed.
6. In a separate bowl, whisk together the dry ingredients—flour, cocoa powder, baking powder, and salt.
7. Gradually add the dry ingredients to the wet ingredients in three batches, mixing gently after each addition. Be careful not to overmix.
8. Evenly distribute the batter into the prepared pans.
9. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out with moist crumbs.
10. Let the brownies cool completely before removing them from the pans and setting them aside.

Cookie Dough Filling:

1. In a stand mixer or large bowl, beat the butter and brown sugar together until light and fluffy.
2. Gradually add the powdered sugar and beat until combined.
3. Mix in the flour and salt, blending until fully incorporated.
4. Add the milk and vanilla extract, then beat until the filling is smooth and creamy.

Ganache Frosting:

1. Heat the heavy cream in a microwave-safe bowl for about 45 seconds, until steaming hot but not boiling.
2. Pour the hot cream over the chopped chocolate or chocolate chips. Let it sit for 30 seconds before stirring slowly with a rubber spatula until smooth.
3. Stir in the corn syrup and vanilla extract until fully combined. Set aside to cool slightly while assembling the cake.

Assembly:

1. Place one layer of the brownie cake on a serving platter. Spoon about 1 cup of cookie dough filling over the top and spread it evenly.
2. Place the second layer on top of the first, pressing down slightly to secure.
3. Spread another 1 cup of cookie dough filling over the second layer.
4. Place the third layer on top, pressing gently to lock the layers together.
5. Chill the assembled cake in the refrigerator for about 10 minutes to firm it up slightly.
6. Once chilled, pour about 1/2 cup of ganache over the top of the cake. Using an offset spatula, spread it gently to the edges, letting it drip slightly over the sides.
7. Add more ganache until the desired coverage is achieved.
8. Return the cake to the refrigerator for 20 minutes to let the ganache firm up.
9. Finally, pipe decorations around the edge of the cake with the remaining ganache and sprinkle with extra chocolate chips.