Position a rack in the center of the oven and heat the oven to 425°F.
Pour the eggs into a blender and blend until thick and frothy, about 3 minutes. Add the milk, granulated sugar, vanilla, salt, and blend just until combined. Sift in the flour and cocoa together, add to blender, and blend on low speed until combined. Alternatively, transfer the egg mixture to a bowl, and whisk in the sifted cocoa and flour.
Heat a 12-inch cast-iron skillet over medium heat until hot, about 2 minutes. Add the butter, and when it begins to foam, add the pear slices, quickly turning them to coat with the butter, and arranging them in a single layer. Pour the batter evenly over the pears and transfer the skillet to the oven. Bake until the pancake is set in the middle, the sides have risen, and the bottom is nicely browned, about 20 minutes.
Sprinkle the pancake with the raspberries and confectioners’ sugar. Serve immediately.