For the spinach, in a heavy 3- to 4-quart saucepan, melt 2 tablespoons of the butter over medium heat. Add the poppy seeds and gently toast until fragrant, about 2 minutes. Add the onion and garlic and cook, stirring, until the onions the onions are almost translucent, but not browned, about 5 minutes.
Sprinkle the flour evenly over the onion mixture, reduce the heat to low and cook, stirring, for about 2 minutes. Whisk in the heavy cream, increase the heat to medium and bring what is now your bechamel sauce to a simmer.
Add the remaining 2 tablespoons butter, one at a time, whisking to incorporate the first one before adding the second. Add the salt, then add the spinach a handful at a time, stirring until the spinach begins to wilt before adding more.
After all the spinach has been added, continue to cook, stirring frequently with a rubber spatula to prevent browning on the bottom of the collapse pan, until the greens completely, about 5 minutes longer. Keep warm while you make the fried Kalettes (optional).
For the Kalettes, bring a large pot of water to a boil. Heat the oil in a pot (2 quarts or larger) to 300°F. Line a sheet pan with a rack or paper towels.
Blanch the Kalettes in a large pot of boiling water for a few seconds and transfer to an ice bath or cool water. Drain well, then transfer to a bowl with ¼ cup of the flour and toss until evenly coated. Add more flour, if necessary, but you really only want a thin coating.
Combine the cornmeal and seasoned salt in a medium bowl and set aside. In a medium bowl, whisk together the buttermilk and egg. Add ⅛ cup water and whisk to incorporate into the batter. Working with 1 Kalette at a time, evenly coat in the batter, then the seasoned cornmeal, setting the breaded Kalettes on a platter.
When the oil is ready, fry the Kalettes in batches until golden brown and crispy, then transfer to the prepared sheet pan. Season with salt and pepper.
Serve the spinach topped with the Kalettes (if using).