Prepare a 9" x 13" sheet pan by greasing or lining with parchment paper or a silicone baking mat.
Mix and bake the red velvet cake per instructions on the manufacturer's box. After baking, cool cake completely.
Using a 2 ¼" cookie cutter, cut out 12 discs from the red velvet cake. Set aside.
Cream Cheese Mousse
Sprinkle gelatin over cold water. Set aside.
Place 1 cup heavy whipping cream in a separate bowl and whip to medium peaks. Place whipped cream in the refrigerator until ready to use.
Place room temperature cream cheese and granulated sugar in a mixing bowl and mix together until combined and no lumps of cream cheese remain.
Melt gelatin until just slightly warm. Stir into cream cheese mixture.
Add whipped cream to cream cheese mixture and fold until completely incorporated.
Fill Silicone Molds
Place the silicone half sphere molds on a sheet pan.
Fill each silicone cavity ¾ full with the cream cheese mousse. Press a red velvet cake disc on top of the cream cheese mousse.
Place in the freezer for 2 hours or until the mousse is set.
Chocolate Ganache
Place the chocolate ganache and softened butter in a heat proof bowl.
Bring ¾ cup heavy cream to a low boil and pour over chocolate/butter. Let set for 5 minutes to allow chocolate and butter to soften.
After 5 minutes, stir the chocolate, butter and cream until smooth. If lumps remain, heat in the microwave at 50% power for 20 seconds and stir until smooth. Repeat as needed.
Finish Cakes
Remove the cakes from the silicone molds and place on a cooling rack. The cakes should easy pop out by pushing up on the bottom of the mold. Allow cakes to defrost for 20 minutes before pouring ganache.
Pour ganache over each cake making certain to cover the entire dome.
Refrigerate cakes until chocolate has set and decorate as desired.