Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking pan.

Make the cake batter: In a large bowl, mix together flour, sugar, cocoa powder, salt, baking soda, and baking powder. Stir in water, oil, and vinegar until smooth.

Bake: Pour batter into prepared pan. Bake for 35–40 minutes or until a toothpick inserted near the center comes out with a few moist crumbs. Let the cake cool completely.

Prepare the cream filling: In a medium saucepan, whisk flour and half & half over medium heat until thickened (3–4 minutes). Remove from heat and stir in vanilla. Let cool completely.

Whip the filling: In a separate bowl, beat softened butter and sugar for 3 minutes. Add cooled flour mixture and beat until fluffy (about 7 minutes). Spread over cooled cake.

Make the ganache: Heat heavy cream in a saucepan until it just begins to simmer. Pour over chocolate chips in a bowl. Let sit for 2–3 minutes, then stir until smooth.

Whip the ganache (optional): Let ganache cool for 30 minutes, then whip for 2–3 minutes until light and airy. Spread over the cream layer.