2Toss the walnuts with the vanilla and scatter them on a foil-lined baking sheet. Bake for 5 minutes, being careful that they don't burn.
3In a bowl, beat the eggs and cream to blend. Add the melted chocolate and beat vigorously until frothy.
4Heat a 10-inch cast iron skillet over medium heat until just hot. Add butter and walnuts and cook for 30 seconds.
5Pour in egg mixture and cook for 1 minute. Transfer pan to the oven and bake until slightly firm, 8 to 9 minutes. Remove from oven and immediately invert omelet onto a 10-inch plate. Dust with confectioner's sugar and cut into wedges.