Make the sauce first. Heat the butter in a saucepan over medium-low heat until it bubbles. Add the green onions and tasso and cook for a minute. Add the heavy cream and Creole seasoning. Reduce by one-third.
While that process is going on, rinse and shake dry the crawfish. Snip the pointy rostrums off the fronts of their heads. Season the flour with Creole seasoning, then dust the crawfish in the seasoned flour.
Combine the milk and eggs. Dip floured crawfish into the mixture and shake off the excess. Dredge them in the seasoned flour.
Heat the oil in a skillet to 350 degrees. Fry the crawfish until golden brown. Remove and keep warm.
Spoon the sauce on warm plates and line up four of the crawfish on each.