Preheat the oven to 400 degrees F. Put two tablespoons butter in a glass 9X13-inch baking dish and pop the pan in the oven while it preheats (if it's taking a while to mix up the batter, keep an eye on the dish so the butter doesn't burn; take it out when the butter is melted).
Combine the eggs, milk and vanilla in a blender and process on low speed until smooth, 10-20 seconds. Add the flour, cocoa powder, sugar, and salt and blend until just combined; the batter should be smooth but take care not to overblend or the pancakes may turn out dense and cakey.
Take the preheated, buttered pan out of the oven and swirl the butter to coat the bottom of the pan. Pour the batter into the pan and immediately return to the oven. Bake for 20 minutes until the pancake is puffy and lightly browned on the bottom and edges.
Serve immediately with sweetened whipped cream, fresh fruit, a drizzle of maple syrup (or whatever else you want to throw on there).
Flour: I have subbed the all-purpose flour for finely ground white whole wheat flour. The pancake is slightly more dense but still delicious.Skillet/Baking Pans: you can experiment making in a cast iron skillet (maybe half this recipe for a 9-inch skillet) or other baking pan; I always use glass but take care when pouring the batter into the hot glass pan (if the batter is chilled at all, it can increase the chances of the pan cracking - you know, hot meets cold and all that; I've never had that happen, but want to give a fair warning).