Recipe(tried): Buttermilk Chess Cake (using cake mix)

Lots of people would call this something like a chess cake, but its not a traditional chess cake with cream cheese...I've nicknamed it the Buttermilk Custard Blondie Somethingorother...LOL...But for here...we'll call it a Chess Cake...

BUTTERMILK CHESS CAKE

FOR THE CAKE BATTER:
1 (2-layer size) box yellow butter recipe cake mix
2 sticks (1 cup) butter, melted, divided use
6 eggs, divided use
I add a small capful veggie oil to the mix (optional)
FOR THE FILLING:
1 1/2 cups buttermilk (I use the whole)
1 1/2 cups granulated sugar
2 tbsp all purpose flour
1 small capful vanilla

Preheat oven to 350 degrees F. Lightly grease a 13x9-inch baking pan (I use the Crisco spray with flour...but however you choose to do it should be just fine).

TO PREPARE THE CAKE BATTER:
Mix the dry cake mix with 1/2 cup melted butter, 2 eggs, and optional oil to form a not too thick not too thin batter/ dough. It will be semi stiff and easy to manipulate. Spread in prepared pan. Set aside.

TO MAKE THE FILLING:
In a large bowl combine the buttermilk, sugar, remaining 1/2 cup melted butter, remaining 4 eggs, flour, and vanilla. Whisking hard for about 2-3 minutes by hand or low speed on a blender for about 2-3 minutes until thick creamy and somewhat frothy...not too much though. Pour over batter in pan.

Bake in oven about 30 minutes until rich golden brown on top...If you start to get worried its burning don't unless you see black spots on top otherwise its fine...when it done remove from oven and allow to cool completely and then refrigerate overnight...

When overnight has come and gone and its ready to slice...You'll notice that the filling you had poured on top is now on the bottom and the cake batter that you put on the bottom is now on the top...So when you slice it...Turn it over so the filling is back on top...(This is all a complete mystery to me??? Maybe I should call it The Mystery Buttermilk Custard Blondie Something or other...LOL...Thats funny...!!!)

I know I know...It looks so good...why can't I eat it now?
Well because the filling hasn't fully set yet the way it needs too...If you eat it warm...Its kind of curdy on the tongue...Trust me...Its better cold...When you can eat it though...you better watch out...You'll find yourself craving it like I do...Even right now as I am writing to share this recipe with you...I am craving the little piece I have left in the fridge...MMMMmmmm...Enjoy!!!

(PS) I've also been thinking about trying this in chocolate...To do the chocolate would be simple I think...
Instead of yellow use a chocolate cake mix and when you get to the filling add a few melted squares of semi-sweet bakers chocolate or 1 to 1 1/2 cups melted semi-sweet chocolate chips to the filling. Everything else would stay the same...If anyone tries this before I do...let me know how it turned out...Thanks!!!