Whip the cream. Whip the cold heavy cream to medium-stiff peaks. Refrigerate it while you do the rest.
150 g cold heavy cream
Beat the cream cheese. Beat the room-temperature cream cheese with the powdered sugar, vanilla, and salt until completely smooth, with no lumps. Any cold lumps will trap the chocolate and turn into specks.
8 oz full-fat cream cheese, room temperature, 30 g powdered sugar, 1 tsp vanilla extract, 1 pinch salt
Melt the chocolate. Melt the milk chocolate gently, in 20-second microwave bursts or over a double boiler. If using a double boiler, pull the bowl off the heat once half the chocolate has melted and let the rest melt from residual heat as you stir. You want it warm, not hot.
3 oz milk chocolate, chopped
Combine. Whisk the melted chocolate into the cream cheese mixture until smooth.
Taste and adjust. Taste and adjust the sugar and salt. It should taste slightly too sweet at this stage, since the cream will mellow it.
Fold in the cream. Fold the whipped cream into the chocolate mixture in 2–3 additions, until smooth and uniform with no streaks.
Fill the cups. Pipe or spoon the filling into the prepared liners.
Chill. Refrigerate at least 4 hours before adding the ganache, ideally overnight, so the filling sets firm.