Chop the couverture into small pieces and pour the warmed cream over them. Stir in the hazelnuts and let everything cool. Shape the mixture into a ball, then freeze it.
Distribute about 2/3 of the hazelnut ice cream evenly in a large bowl lined with clear plastic food wrap and press the chocolate-hazelnut ball into the center. Add the rest of the ice cream on top. Spread the topmost surface flat with a spoon and then freeze the whole thing again.
Heat some water in a pan. While that's warming up, put the egg whites, sugar, water, and salt in a bowl, put the bowl on top of the pan, and beat the mixture with an electric whisk until it's stiff. Take the bowl off the pan and set it to one side.
Turn the ice cream dome out onto a serving platter and pull away the plastic food wrap. Use a spatula to spread the egg white cream evenly over the entire dome. Then put the whole thing back in the freezer.
Let the chopped milk chocolate and the coconut oil melt over a water bath and stir them together to form a glaze. Pour it over the Ice Cream Praline. Chill one last time before serving.