Heat your oven to 350.
Grease and Flour a 9x13 glass baking dish or aluminum pan.
In a large mixing bowl, combine the melted butter with the sugar and the vanilla.
Gradually add the cocoa powder and salt and whisk until smooth.
Add the food colouring and the vinegar and combine.
Add the eggs and the flour and mix until smooth.
Set about 1/4 c of this batter to the side.
Spread the remainder of the batter evenly into the baking dish or pan.
In a medium mixing bowl, whisk the cream cheese until smooth.
Add the white sugar and whisk again.
Add the eggs and the vanilla and stir until the mixture is as smooth and glossy as you can get it.
OPTIONAL: add a few drops of White-White if you think the topping is too yellow.
Carefully pour the cream cheese batter evenly over the top of the red velvet batter.
With an icing spreader or a spatula, gently spread the cream cheese batter out evenly without pulling up the red from the bottom.
With a skewer or chopstick, carefully trace the outlines of 24 squares in the top of the cream cheese batter.
With a skewer or chopstick, drop two dots of red batter into each square, towards the top third of each square.
Then, use the skewer or chopstick to drag some of the red icing down, creating the effect of two red punctures dripping blood in each square.
Bake for about 40 minutes.
Slice into 24 squares.
Store, wrapped, in the refrigerator if desired.