Preheat oven to 350 degrees.
In a large bowl, combine butter, sugar, and eggs with a mixer (using a paddle attachment if you have one...if not no worries) for about 1 minute or until well blended. Mix in apple cider and and mix until just blended.
In a separate bowl, combine flour, baking powder, nutmeg, and salt. Working in small batches, mix the flour mixture into butter mixture until all of the flour mixture has been added to the butter mixture and is well blended.
Divide dough in half on a floured piece of parchment paper. Shape each dough-half into a long roll shape, about 12-14" long.
Carefully lift rolls onto a baking sheet, 3-4 inches apart from each other. With your fingers, press down on each “log” so that they end up being about a ½" high.
Bake for 25 minutes or until golden brown.
Carefully lift the parchment paper from the baking sheets and place on your cooling racks.
Set aside your baking sheet, as you will use it again.
When biscotti had cooled enough to handle, yet are still warm, carefully move them to a cutting board and cut crosswise slices (approximately ½" in size).
Place slices, cut side down, back on original baking sheet. Bake for 10 minutes. Then remove from oven and turn slices over. Bake for another 10 minutes or until somewhat firm and lightly browned.
Transfer to wire racks to completely cool, with tops facing up.
In a small bowl, mix together powdered sugar, apple cider and cinnamon. If needed, add more cider or powdered sugar to achieve desired consistency (you don't want it too runny, since you want it to firm up on thebBiscotti).
Space biscotti pieces no more than ½ inch or so apart from each other on either a wire rack or parchment paper (hello easy clean-up) dip a metal whisk into the glaze, allowing some of the excess to drip off. Then quickly drizzle back and forth, back and forth across sections of your Biscotti Continue until they are glazed as you like. You can also place glaze in a small plastic baggie, snip off one end and drizzle the glaze from there, your choice.