Preheat oven to 176C.
Line your 8x8 inch pan. I used a 10x6.
In your mixing bowl, beat sugar and butter until light and fluffy.
Add cocoa powder, beat until combined.
Add red food colouring, vinegar, and vanilla extract.
Mix to combine, then add in eggs.
Beat to combine and add flour.
Mix until combined.
Reserve about 1/4 cup batter for swirling.
Pour the batter into lined pan, and smooth out the top.
Then prepare cheesecake batter.