Cheesecake brownies

This is a heavenly chocolate recipe - dense, rich brownies paired with a not-as-sweet, creamy cream cheese mix.  The chocolate and the cream cheese balance each other out - that's the key.  Adapted from a Cooks Illustrated recipe, per this website.  Note: I can't get unsweetened baking chocolate in the UK, so I've substitute cocoa powder and butter, per the conversion on this website, it worked just fine.

Ingredients

For the brownie batter

2/3 c flour
1/4 t salt
1/2 t baking powder
120 g bittersweet chocolate (I used 85% cocoa chocolate)
35 g cocoa powder
125 g lightly salted buter
1 c sugar
2 t vanilla extract
3 large eggs

For the cheesecake batter

450g cream cheese (at room temperature)
1 egg yolk
1/4 c sugar
1 t vanilla extract

Instructions

1) Preheat oven to 165C/325F.  Coat the bottom of an 8" square baking pan with baking spray, lay down an 8x16" piece of foil to coat the bottom and sides (folding over the sides for handles), and coat the inside of the foil with baking spray.
2) Whisk cocoa powder, flour, salt, and baking powder in a small bowl and set aside.
3) Combine bittersweet chocolate and butter together in a microwave-safe bowl, and melt gently until silky smooth.
4) Whisk in 1 c sugar, 2 t vanilla, and eggs (one at a time).
5) Whisk in dry ingredients, mixing until just incorporated - do not overmix.
6) In another bowl, mix cream cheese, 1/4 c sugar, 1 t vanilla, and egg yolk.
7) Pour half of brownie batter into prepared pan, then drop half the cream cheese mixture throughout the batter in spoonfulls, distributing evenly. Swirl cream cheese mixture through batter with a a table knife or spoon.
8) Pour remaining half of brownie batter into pan, drop remaining cream cheese filling throughout, and swirl, creating a marbled effect.
9) Bake in oven for 50-60 minutes, until brownies have puffed slightly, and a knife inserted into the middle comes out with moist crumbs (or a tiny amount of batter).  The center should feel not quite firm - it's better to have them come out undercooked than overcooked.  Cool 5 minutes before eating.