Preheat over to 350F. Melt your butter in a small saucepan and set aside.
In a bowl mix your sugar, buckwheat flour, cocoa, baking powder and salt.
Make a well in the middle of the dry ingredients and crack two eggs into it. Then I get my Danish dough whisk, you could use a fork or a wooden spoon, and start mixing the eggs as I pour the melted butter. Mix the batter together until well combined.
Spread all but about ½ cup into a greased 8x8 pan. Reserve that ½ cup for topping.
In the small saucepan I used to melt the butter, I measure in all the cheesecake batter ingredients. Use the same whisk you used to mix the brownie batter, without washing it, It's not a big deal. Mix well, then spread on top of the brownie batter.
Then take the reserved brownie batter and dot it all over the top of the cheesecake batter. If you forget to reserve batter, or choose to skip doing so, it's just for looks anyway.
Bake at 350 °F for about 35-40 min, or until a butter knife inserted comes out clean.
Let cool before cutting, they can be a little crumbly if still warm but hey, serve on a plate with a fork and nobody is going to complain about a warm cheesecake brownie!