In a small microwave-safe bowl or a saucepan, melt the 55g of butter in short bursts in the microwave or over low heat on the stovetop until completely liquid. Set aside to cool slightly.

Combine the melted butter and Oreo cookie crumbs. Mix until all the crumbs are evenly moistened and resemble wet sand.

Pour the mixture into the prepared pan. Using the bottom of a glass or a flat measuring cup, press the crumbs firmly and evenly into the base. Refrigerate for at least 30 minutes to set.

In a small bowl, soak the gelatin sheets in plenty of cold water for 5-10 minutes until soft and pliable.

In a large bowl, mix the softened cream cheese with the granulated until completely smooth, creamy, and free of any lumps.

Pour in the cold heavy cream and stir until the mixture is combined and thickened slightly (it will look like a very thick, spreadable frosting). Be careful not to over-whip.

Squeeze the excess water from the softened gelatin sheets. Place them in the hot milk and stir until the gelatin is completely dissolved and no strands remain.

While whisking the cheesecake mixture constantly, slowly pour in the warm gelatin-milk mixture. Whisk until everything is fully incorporated and the batter is uniform. This is your base mousse batter.

Divide the base mousse batter evenly into two bowls.

Take one portion and pour it directly onto the chilled Oreo crust. Smooth the top with a spatula. Place the pan in the freezer for 25-30 minutes, or until the surface is completely set to the touch. This quick-freeze step is key for clean layers.

While the first layer sets, add the strawberry jam to the second portion of base mousse batter. Fold gently until the jam is mostly incorporated, leaving some streaks if desired.

Once the first layer is firm, remove the pan from the freezer. Gently pour the strawberry mousse batter over the top and spread it evenly. Give the pan a few gentle taps on the counter to release any air bubbles.

Carefully transfer the cake to the refrigerator. Chill for at least 4 hours, or preferably overnight, to allow it to set completely.

To serve, run a thin knife warmed with hot water around the edge of the pan before releasing the springform clasp. Decorate the top with piped whipped cream and fresh strawberries, if desired. Slice with a hot knife for clean cuts.