Whisk together the two flours and salt in a large bowl. Whisk the buttermilk and eggs together in another bowl. Pour the wet ingredients into the flour and mix well with a fork until you get a sticky batter.
Cover and let this sit on the counter for at least 30 minutes, to allow the flours to hydrate.
Bring a large pot of salty water to a boil. Using a spätzle maker, a coarse grater, colander or other device with large holes, drop the spätzle dough into the water in little bits. Boil for 1 to 2 minutes after they all rise to the surface.
If you are eating them now, they’re ready. To hold for up to a day or so, plunge the spätzle into a large bowl of ice water to stop the cooking. Drain and toss with a little oil, then set out on a sheet pan for up to a few hours, or in a covered container for a day or two.
I prefer to serve my spätzle by frying in a bit of butter after they're all made and chilled. Heat maybe 1/4 cup of butter in a large, wide pan and lay the spätzle down on it. Toss to combine, then let the spätzle brown a bit by not moving them for about 90 seconds. Remove from the pan and serve hot.