In a medium skillet, add the butter and melt over medium high heat. Add the onion and rosemary and season with salt and pepper. Cook until softened, 5 minutes, then add the jalapeño and cook for 2 minutes, then add the white wine and stir until reduced, 2 minutes.
Add the flour and cook for 2 minutes, then slowly stream in the heavy cream, stirring constantly, until the flour is dissolved. Add the sour cream, lemon zest, and nutmeg. Bring to a simmer, then add the kale and cover, stirring a few times, for 8 minutes, or until just wilted. Remove from the heat, add the cheese and stir to melt, 3-4 minutes.
Make the panko topping:
In a small skillet, melt the butter and add the pepper and rosemary. Cook until fragrant 2 minutes. Add the panko and continue cooking, stirring frequently, until golden. season with a pinch of salt, stir in the walnuts, then remove from the heat.
Plate the creamed kale in a bowl and top with the Panko walnut topping and serve!