Melt 2 tablespoons unsalted butter in a medium microwave-safe bowl in 20-second bursts until mostly melted, 40 to 60 seconds total (it will melt completely as it sits). (Alternatively, melt the butter in a small saucepan over medium heat and pour into a medium bowl.) Set aside to cool slightly.

Twist 21 of the Oreo cookies apart to separate them. Scrape the cream into a stand mixer bowl or large bowl if using an electric hand mixer. Place 18 of the cookie halves in a large zip-top bag. Seal the bag and crush with a rolling pin into fine crumbs (about ¾ cup).

Add the Oreo crumbs and 1 pinch of the kosher salt to the butter and stir to combine. Divide the Oreo crumbs between 4 (6- to 8-ounce) glasses, jars, or ramekins (about 3 tablespoons each).

Add the remaining 24 cookie halves to the same large zip-top bag. Seal the bag and tap with the rolling pin into small-medium pieces. Do not crush into fine crumbs.

Add 2 ounces cream cheese, ½ cup of the powdered sugar, 1 teaspoon vanilla extract, and 1 pinch of the kosher salt to the cookie cream. Beat with the paddle attachment on medium speed until smooth and fluffy, 1 to 2 minutes. Add 1 ½ cups of the cold heavy cream. Beat on medium-high speed, scraping down the sides and bottom of the bowl about halfway through with a flexible spatula, until medium peaks form, 4 to 6 minutes.

Add the broken cookie pieces. Gently fold with a flexible spatula until just combined. Do not overmix or the color of the mousse will turn gray.

Place the remaining ½ cup cold heavy cream, remaining 1 tablespoon powdered sugar, and remaining 1 pinch kosher salt in a medium bowl (or transfer the contents of the stand mixer bowl to another bowl to reuse it). Beat with the whisk attachment on medium to medium-high speed or whisk by hand until soft peaks form, 1 to 2 minutes.

Divide the mousse over the crumbs (generous ½ cup each). Divide the whipped cream over the mousse (generous ¼ cup each). Refrigerate for at least 2 hours or up to overnight.

When ready to serve, cut the remaining 2 Oreo cookies in half crosswise and garnish each mousse with a piece.