Melt white chocolate in the microwave until smooth. Allow to cool slightly.

In the well-chilled bowl* of a stand mixer fitted with a whisk attachment, beat the heavy cream until soft peaks form. Gradually add powdered sugar and continue whipping until stiff peaks form. Transfer whipped cream to another bowl and place in refrigerator to keep chilled.

Return bowl to mixer. Switch whisk attachment out and replace with paddle attachment. Beat cream cheese until smooth. Add melted white chocolate and continue beating until light and fluffy.

Add a quarter of the whipped cream and beat until combined. Remove bowl from mixer and use a spatula to fold in the remaining whipped cream. Transfer mousse to a pastry bag or a gallon-sized ziploc bag with the tip of the corner cut off.

To layer: Place a layer of cake cubes in the bottom of each jar. You'll use half of the cake. Then pipe half of the chocolate mousse into each jar. Crumble two Oreos into each jar. Add another layer of cake cubes (using up the last half of the cake), followed by the rest of the chocolate mousse. Garnish each jar with one more Oreo and sprinkles.