Place chocolate in a large bowl set over a double boiler (glass bowl over a pot of water) at a low simmer. Stir chocolate until melted. Turn off the heat and let stand.
Whip the cream until it forms soft peaks. Set aside and hold at room temperature. With a mixer, whip egg whites to soft peaks. Gradually add the sugar and continue whipping until firm.
Fold the egg whites into the melted chocolate. When the whites are almost completely incorporated, fold in the whipped cream. Cover the mousse and refrigerate for approximately 1 hour or until set.
Decorate the ice cream cones. Melt the chocolate chips and schemer it on the top 1" of the cone. Roll in the sprinkles.
When ready to serve, fill in the cones with the mousse and top with sprinkles.
Notes
You can make the mouse "tops" of the cones ahead of time. Divide the mousse into two piping bags and fit one with a Wilton 1M piping tip. Pipe pout on to was paper over a cookie sheet and place in the freezer until ready to serve.