Lightly grease a 9-inch deep-dish pie plate or a 9-inch springform pan with a little butter or nonstick spray. A springform pan makes it easier to slice and serve neat pieces.

Place the Oreo cookies in a food processor and pulse until you have fine crumbs with no large chunks. Alternatively, seal the cookies in a zip-top bag and crush them with a rolling pin until finely ground. In a bowl, mix the cookie crumbs with the melted butter and a pinch of fine sea salt until the mixture resembles wet sand.

Pour the crumb mixture into the prepared pan. Use the bottom of a measuring cup or glass to press it firmly into the bottom and slightly up the sides. Pack it down well to help prevent crumbling when sliced. Freeze the crust for at least 15–20 minutes while you prepare the filling layers.

Gently warm the hot fudge topping in the microwave or in a small saucepan over low heat until it is pourable but not hot. If the fudge is very thick, whisk in the heavy cream until smooth and spreadable so it won’t tear up the crust.

Remove the chilled crust from the freezer and pour the warm fudge over the bottom. Spread it into an even layer with an offset spatula or the back of a spoon, keeping it mostly in the center and not too far up the sides. Freeze again for about 15 minutes, until the fudge firms slightly.

While the crust chills, let the coffee ice cream sit at room temperature for 10–15 minutes until scoopable and easy to spread but not melted. If using instant espresso powder, stir it into the softened ice cream. Fold in the chopped toasted pecans or walnuts if you’re using them.

Spoon the softened ice cream in small scoops over the firm fudge layer. Gently press and spread the ice cream to an even layer, trying not to disturb the fudge beneath. Smooth the top with a spatula. Cover tightly with plastic wrap or foil and freeze for at least 4 hours, or until very firm, preferably overnight.

About 30–45 minutes before serving, combine the cold heavy whipping cream, powdered sugar, cocoa powder, vanilla extract, and a pinch of salt in a large chilled bowl. Using a hand mixer or stand mixer on medium-high speed, whip until medium-stiff peaks form and the mixture looks like a soft chocolate cloud. Do not overwhip or it may become grainy.

Remove the frozen mud pie from the freezer. If using a springform pan, release and remove the sides. Spread or pipe the chocolate whipped cream over the ice cream layer, leaving a small border around the edge if you’d like the layers to show. Sprinkle with extra crushed Oreos or graham crumbs, shaved chocolate or mini chips, roasted nuts, and/or drizzle with additional hot fudge or chocolate syrup.

For the cleanest slices, place the finished pie back in the freezer for another 30–60 minutes after adding the whipped cream. When ready to serve, let the pie sit at room temperature for about 10–15 minutes. Use a sharp knife warmed in hot water and wiped dry between cuts to slice and serve.