In a large bowl, mix the flour and salt together. Whisk in the milk, cream, butter and egg until smooth. Cover the bowl and refrigerate, about 1 hour.
Add a pat of butter to a 10-inch nonstick skillet over medium-high heat. Add 2 ounces of the batter and swirl around to coat the skillet in an even thin layer. Cook until light golden brown, about 1 minute. Flip the crepe with a fish spatula or thin turner and cook, 15 to 45 seconds. Transfer the crepe to a plate and repeat with the remaining batter, adding more butter if needed.
Spread each crepe with a generous helping of chocolate spread, slices from half a banana and a handful of potato straws. Roll up, closing off both ends and cut on a bias. Serve dusted with powdered sugar.