Line an 8x8-inch baking pan with 2 sheets of parchment paper, positioning them perpendicular to each other, leaving about 2 inches of overhang.

Whisk together the instant chocolate pudding mix and cold milk in a large bowl until dissolved and slightly thickened, about 2 minutes. Let sit to thicken.

Break the graham cracker sheets into rough pieces and place in a food processor. Add 2 tablespoons granulated sugar and 1/4 teaspoon kosher salt, processing until the texture resembles sand, about 15 seconds.

Add the melted unsalted butter to the cracker mixture and pulse to combine, 6 to 8 times for 1 second each. If using graham cracker crumbs, stir the crumbs and butter together in a medium bowl.

Transfer the mixture to the pan and press it into an even layer, reaching the edges and filling the corners. Refrigerate while preparing the filling.

Beat the cold heavy cream and 1/4 cup powdered sugar in a stand mixer with the whisk attachment on high speed until stiff peaks form, about 2 to 4 minutes. Transfer to another bowl.

In the stand mixer (no need to clean), beat the cream cheese, ricotta cheese, remaining powdered sugar, orange zest (if using), vanilla extract, and remaining kosher salt with the whisk attachment on medium speed, scraping the bowl halfway through, until light and fluffy, about 3 minutes.

Gently fold 1 cup of the whipped cream and 1/2 cup of miniature chocolate chips into the cream cheese mixture until combined.

Dollop the cream cheese mixture over the crust and spread into an even layer. Dollop the chocolate pudding over this layer and spread evenly. Finally, dollop the remaining whipped cream over the pudding and spread into an even layer.

Cover and refrigerate for at least 4 hours or up to overnight. Before serving, sprinkle the remaining 1/4 cup miniature chocolate chips evenly over the top.

Grasp the parchment overhang to transfer the slab to a cutting board. Cut into 12 pieces, wiping the knife between cuts for cleaner slices.