Place a 12-inch skillet over medium
heat. While the pan gets hot, in a
large bowl, combine the flour blend,
xanthan gum and salt. Add the
eggs and butter, mixing well after
each addition. In a slow and steady
stream, whisk in the milk. Continue
mixing until the batter is pourable
and not very elastic. Add more milk
if necessary to reach the desired
Ladle ¼ cup of the batter into
the hot skillet, swirling to spread
evenly. Cook until set but not
crispy, about 1 to 2 minutes, then
flip with a wide spatula. Cook
on the other side for another 30
seconds. Transfer to a plate and
cover with a moist towel. Repeat
with the remaining batter.
In the hot skillet, combine the
spinach with ½ teaspoon water.
Reduce the heat to medium
and continue cooking, covered,
until the spinach is wilted, 1 to 2
minutes. Transfer to a paper-towel-lined plate.
Remove the first warm crepe
from under the towel, lay it flat on a
plate, and layer a slice of prosciutto,
a sprinkling of cheese and some
of the wilted spinach across the
center. Fold into thirds. Repeat with
the remaining crepes and fillings.