Make the white chocolate cream cheese bark. Melt white chocolate VERY GENTLY in a heatproof bowl set over a saucepan with very hot, barely simmering water. Let it melt slowly with occasional stirring. Cut cream cheese into cubes and place it in a medium bowl. Make sure it is very soft. Add melted chocolate over it and use a sturdy whisk to mix it together until it looks smooth and glossy. You don’t want to incorporate too much air, but you do need to whisk well so it comes into an emulsion. The mixture will thicken up. Scrape it onto a parchment-lined baking sheet and spread it out to about ⅛ or ¼ inch thickness. It’s ok if it looks a bit chalky and maybe looks matte at this point.
Place it in the freezer for about 30 minutes until firm. Once firm, peel off the parchment and quickly slice the bark into about ¾ inch squares or pieces (the size or shape doesn’t matter too much, but I like to keep them on the larger side since they are soft and will break up as you scoop the cookie dough). Place the pieces back in the freezer until you are ready to add them to the cookie dough.
Melt chocolate. Combine butter and chocolate in a heatproof bowl and melt in the microwave, then stir until smooth and glossy. You can also melt it gently in a saucepan over the stove. Add cocoa powder, vinegar and salt and whisk to combine.
Combine egg, yolk, and sugar in a large bowl and whisk vigorously by hand until pale and creamy-looking. You can also use a hand mixer or a stand mixer fitted with the whisk attachment. Mix in sour cream, vanilla and red food coloring. Add the warm chocolate mixture and whisk to blend well.
Sift in the flour and fold it in gently. Add the chilled white chocolate cream cheese wafers and fold them in. Reserve a few extra for topping if you’d like. Spread the batter into the prepared pan and place reserved wafers on top. Use a small offset spatula to spread some of the batter over the wafers to nestle them in.
Bake for 25-28 minutes until the top is glossy and the edges feel set and skewer inserted into the center comes out with a few sticky moist crumbs attached. Do not over-bake these or they will be dry.
Transfer pan to a wire rack and let brownies cool completely in the pan. Refrigerate for at least 1 hour before lifting out and cutting into squares.