Heat-treat the 2 cups of flour by spreading it on a baking sheet and baking at 350 °F (177 °C) for ~5–10 minutes until it reaches ~160 °F internal, then let cool. This makes it safe to eat raw. ([source on edible cookie dough techniques])

Preheat your oven to 350 °F (177 °C). Grease and line cake pans (e.g. 2 or 3 pans) with parchment and flour.

In a large bowl, whisk together flour, sugar, cocoa, baking soda, baking powder, and salt for the cake.

Add eggs, buttermilk, oil, and vanilla; mix until combined. Then stir in hot water (or coffee) to create a thin batter.

Divide batter among pans. Bake for ~20–30 minutes or until a toothpick comes out clean. Let cakes cool completely on racks.

Meanwhile, make the edible cookie dough: Cream the softened butter, brown sugar, granulated sugar until light. Mix in vanilla and milk. Gradually add the heat-treated flour until combined, then fold in mini chocolate chips. Chill if needed to firm texture.

For the cookie dough buttercream: Beat softened butter and brown sugar until creamy. Add powdered sugar gradually, along with vanilla and milk, until you reach frosting consistency.

Make the chocolate ganache: In a small saucepan, heat cream until just simmering, pour over chopped chocolate, let sit ~30 seconds, then whisk until smooth. Let cool to slightly thick but pourable consistency.

Assemble the cake: Place one cake layer on your stand or plate. Spread a layer of cookie dough buttercream, then crumble some edible cookie dough onto it (press lightly). Add next cake layer, repeat. After stacking, crumb coat with buttercream and refrigerate ~15–30 minutes.

Frost the cake fully with the remaining buttercream. Pour the chocolate ganache over the top to drip down the sides. Let set.

Optionally, roll small pieces of cookie dough into decorative balls and place them atop the cake, or sprinkle extra cookie bits.