Combine 1 1/2 cups graham cracker crumbs, 1/4 cup milk powder and 1 teaspoon kosher salt in a medium bowl, whisking together until well combined.
In a liquid measuring cup, whisk together 4 tablespoons unsalted butter and 1/4 cup heavy cream. Add to the dry ingredients (from the 1st step) and use a rubber spatula to toss again until the mixture comes together — the butter and cream will act as a glue and create small clusters.
Transfer the clusters to a 9-inch deep pie plate and use your fingers and the palms of your hands to press the crust firmly into the pie plate, covering the bottom and sides of the pan completely. The crust is easiest to mold just after mixing. Set aside as you make the chocolate mascarpone filling.