In a medium saucepan over low heat, whisk together milk, sugar, and egg yolks until smooth—about 3 minutes. Stir constantly; you want it warm, not scrambled.

Remove from heat and stir in chocolate chips, butter, and salt. Let sit for 1–2 minutes, then whisk until silky. If there are a few stubborn chips, a brief 10-second zap in the microwave helps.

Stir in vanilla extract, then let the chocolate custard cool at room temp for about 5 minutes (you don’t want it scalding when you fold in the cream).

Using an electric mixer on medium-high, whip the chilled heavy cream until medium peaks form—soft enough to fold, firm enough to hold shape.

Transfer whipped cream into the chocolate custard in three additions, folding with a spatula in slow, sweeping motions to keep the mix airy.

Spoon the chocolate filling into your graham cracker crust, smoothing the top with an offset spatula or the back of a spoon.

Cover loosely with plastic wrap and refrigerate for at least 2 hours (overnight is even better for a firmer slice). You’ll know it’s set when a light jiggle at the center feels more like a gentle wobble.

Top with extra whipped cream, shaved chocolate, or fresh berries just before slicing. A sharp, warm knife makes clean cuts—dip the knife in hot water and wipe dry between slices.