Gently melt the chocolate and butter either using a double-boiler set over simmering water or using a heavy-bottomed pot over very low heat. Stir to combine and once melted, set aside to cool.
Scrape the cooled chocolate mixture in the bowl of a standing mixer.
Add the eggs, sugar, vanilla and salt and mix well.
Add the flour to the brownie batter and beat until smooth.
Pour ¾ of the brownie batter into the prepared pan and smooth the top using a knife or spatula dipped in water. Set aside the remaining ¼ of the batter.
If you only have one bowl for your standing mixer, wash and dry it. Alternatively, you can use a handheld mixer for the cheesecake layer.
To make the cream cheese layer, beat together cream cheese and sugar.
Add the egg, flour and vanilla and food coloring (if using) and mix until smooth.
Drop dollops of the cheesecake batter on top of the brownie layer until almost covered.
Drop dollops of the remaining brownie batter on top of or in between the dollops of cheesecake batter.
Draw knife through the layers of brownie and cheesecake batter to swirl them. (If they are not swirling well, try baking them for five minutes and trying again.)
Sprinkle top with white chocolate chips (if using.)
Bake for 30 to 35 minutes until cheese cake layer is almost set.
Cool pan on a cooling rack prior to cutting.
Recipe by West of the Loop at https://www.westoftheloop.com/2014/02/01/valentines-day-cheesecake-brownies/