1. Put all ingredients into a blender and blend for about 30 seconds at half speed.
2. Or mix eggs and flour by hand or in a mixer adding cocoa and sugar and then milk gradually, beating all the time.
3. Add vanilla and cooled, melted butter and beat once more.
4. Let stand covered an hour or two. Heat a small skillet or crepe pan--about 5 inches in diameter, brush with butter and when butter bubbles up, pour about 1 1/2 tablespoon of crepe batter into pan, swirling so batter covers the pan.
5. Cook for about 1 minute, check for browning and watch carefully--both the cocoa and sugar cause crepes to burn easily.
6. Turn crepe over and cook for about a half minute on the other side.
7. Turn out on paper towels. This recipe will make from 18 to 24 crepes depending on the size of the pan and amount of batter used for each crepe.
8. These freeze well. Variations: Add 1/2 cup finely grated almonds, walnuts, or hazelnuts to the batter just before cooking the crepes.
9. Or add 1 to 2 tablespoons of creme de cacao to the batter and mix well.
10. Suggested Uses: Cocoa crepes go well with many of the dessert crepe fillings, especially pastry cream, whipped cream, ice cream, apricots, sugar, and nuts.