How could I "unleaven" it for Passover. Almost seems perfect for then
I think it's already unleavened & ok for passover - there's no leavening agent in the crepe batter or the filling.
The problem lies with the flour. To be suitable for Passover, you can't use regular flour -- it has to be "Kosher for Passover." You can buy Matzo Cake Meal (same places that sell matzo), which should work. I think you should try making the crepes with the basic ingredients to test it, because it probably does not have the same characteristics as AP flour. It may need more or less liquid, and probably would have to rest for a couple hours (as the recipe says). If the test batch works, then you could go ahead. Sounds wonderful, doesn't It?
Here's a link for "Passover crepes." You might want to use one of these recipes for crepes and add the cocoa, spices, etc. from the food52 recipe.
My mother used this recipe for blintzes, year round. It's given as a Passover recipe in Love and Knishes, by Sara Kasden. For the blintz (crepe) -- Mix 1/2 cup potato flour, 1/2 cup matzo cake meal, 1/2 tsp salt. Beat 6 eggs until light, add 1/2 cup water, beat in. Gradually add 1 cup water to the flour mix, until smooth. Add beaten eggs to the batter, stirring in slowly.
I'd go with the blintz recipe, but isn't there a stipulation that to be kosher for Passover, the flour/matzo meal has to go from its dry state to completed product in 18 minutes? You certainly couldn't let the blended mixture in the original recipe rest even if you didn't use flour, and making blintzes in 18 minutes would be cutting it pretty closely.
I believe there are 2 issues here -- the matzo meal I'm likely to see in stores only appears at Passover, made from matzo that has to be in the 18 min parameter (because fermentation will start as the dough rests), so those boxes will be labeled Kosher for Passover.
2nd, what happens to it in the baking/cooking process -- maybe someone else can answer whether the clock is running on that. The recipe I give does not sit/rest -- it is used when it is made. Sustan, If you have a Kosher home, you will follow the requirements; if not, you will not have those concerns.
The recipe calls for 'potato flour,' but I assume that it uses potato starch (which is not the same as flour, to be precise). That's what I'm familiar with for Passover baking, and what I think was in my mother's kitchen.
The matzoh cake meal you find at this time of year is likely to be labelled kosher for Passover. The eighteen-minute law only applies to that product, not to the length of time for making the recipe or resting the batter. Standard flour can't be used on Passover. So if you sub either the KLP matzoh cake meal or potato starch, that is not a problem. You would have to sub something for the rum and the vanilla: All manufactured products should be kosher for passover, especially products with alcohol (even though rum is based on fermented sugar). It seems doable, though.
I'm not sure cake meal will work well, or at least it will taste differently. It has a very distinct flavor that tastes like matzoh. Some people eat rice on Passover. If that's an option, I would try rice flour. As far as the 18 minutes, as creamtea notes, that does not apply to recipes you are making but to the matzoh itself when it is initially made. Anything that is kosher for passover can be used in any way, regardless of how long it takes to make the dish. Smitten Kitchen has many passover desserts on her website as does the NYT and epicurious. Flourless chocolate cakes are always a safe bet.