Preheat oven to 320°F (160°C). Grease a 12-cup muffin tin well. Place a large roasting pan in the oven and boil water for a water bath.

Over a double boiler, melt the cream cheese, butter, and milk together, whisking until smooth and lump-free. Remove from heat and cool slightly.

Whisk the egg yolks, vanilla, and lemon juice into the warm cheese mixture. Sift in the cake flour, cornstarch, and 2 tbsp sugar. Whisk gently until just combined.

In a clean bowl, whip egg whites until frothy. Add cream of tartar. Gradually add the 6 tbsp of sugar, whipping until soft to medium peaks form.

Gently fold the meringue into the cream cheese batter in three additions, using a spatula to carefully fold until no white streaks remain. Do not overmix.

Divide the batter evenly into the prepared muffin tin.

Place the muffin tin into the roasting pan in the oven. Carefully pour boiling water into the roasting pan until halfway up the muffin tin sides.

Bake at 320°F for 20 minutes, then lower the temperature to 280°F and bake for 15 more minutes until golden on top.

Turn the oven off, crack the door slightly, and let the cupcakes cool inside for 15 minutes to prevent sinking.

Remove from water bath, cool completely, and chill in the fridge for 2 hours. Whip heavy cream with powdered sugar, pipe onto cupcakes, top with a blackberry, and dust with powdered sugar.