I made a blackberry mousse cake for my brother's birthday this year, and I happened to have enough components left over to make a couple of individual mousse cakes as well! I just used my 3-inch cake rings (similar to these) to assemble them. (I've also used these rings to make these individual triple chocolate mousse cakes, and they're great for making tuna tartare as well!)
I divided the chocolate crust mixture between the cake rings, and then used a shot glass to pack the mixture down before baking them at 350F for about 7 minutes. Then when the crust had cooled, I just poured on the middle cheesecake layer, let it set in the fridge for an hour, and then poured on the blackberry mousse layer on top of that. (See here for more on the layers.)
I let the cakes set overnight, and then carefully unmolded them before topping them with a few fresh blackberries.
And there you have it - a simple. delicious, and (mostly) no-bake dessert!