Chill your serving vessels (6 small jars or 6 × 6‑oz ramekins) in the refrigerator while you work. Cold ramekins help the filling firm up faster when returned to the fridge and give a clean presentation.

Make the crust: melt 3 tablespoons of the butter in a small saucepan over low heat. Mix the melted butter with the 1 1/2 cups crushed graham crackers and a pinch of salt until the crumbs are evenly moistened. Press about 2–3 tablespoons of the crumb mixture firmly into the bottom of each chilled ramekin. Pressing creates surface tension so the crust binds and holds its shape without baking; chilling next firms the butter so the crust stays crisp.

Set up a double boiler (bain‑marie): place a medium heatproof bowl over a saucepan of gently simmering water (the bowl should not touch the water). This gentle indirect heat is used to cook the eggs slowly so they thicken without scrambling—key for a silky custard.

Combine the eggs and sugar in the heatproof bowl. Whisk vigorously to blend. Place the bowl over the simmering water and whisk constantly for 4–6 minutes until the mixture is pale, slightly thickened, and registers 160°F (71°C) on an instant‑read thermometer. Heating to 160°F pasteurizes the eggs and dissolves the sugar while creating a stable, light zabaglione base—this is what gives the filling a glossy, airy silkiness once chilled.

Remove the egg‑sugar mixture from the heat. Let it cool for 1 minute, then whisk in the cream cheese (1/2 cup at a time) until fully incorporated and smooth. Adding the cream cheese off the heat prevents it from breaking and keeps the texture velvety. If you get small lumps, a brief blitz with an immersion blender (20–30 seconds) will smooth it right out.

Whisk in the remaining 1 tablespoon softened butter, the milk, vanilla extract, lemon zest (if using), and the 1/8 tsp salt. The butter adds richness and sheen; milk loosens the mixture to a spoonable consistency. Taste and adjust: add a touch more lemon zest or a pinch more salt to brighten or deepen flavor.

Divide the filling evenly among the prepared ramekins on top of the chilled crusts. Smooth the tops with an offset spatula or the back of a spoon. Using individual pots chills faster and looks elegant for serving—no slicing required.

Cool briefly on the counter (10–15 minutes) to let residual heat dissipate, then cover each ramekin loosely with plastic wrap and refrigerate for at least 1 hour until set. Chilling lets the zabaglione‑based filling fully thicken and the flavors meld. For best texture, chill 2–3 hours or overnight—the filling becomes denser and creamier with time.

Serve chilled as‑is, or top with a quick garnish: fresh berries, a drizzle of honey, toasted nuts, or a spoonful of fruit compote. The contrast of the crisp, buttery crust and the cool, silky filling is what makes this dessert feel like a restaurant‑quality cheesecake without using an oven.