Prepare the Kale: Rinse the kale well.
Remove and discard the thick stems and ribs. Roughly chop the leaves and place them in a large pot with a few tablespoons of water.
Cover and steam until wilted and tender, about 5 minutes. Be careful not to overcook.
Drain in a colander and set aside to cool.
Cook the Lasagna Noodles: Fill the same pot with water, add 1 tablespoon (15 ml / 0.5 fl oz) of oil, and bring to a boil.
Cook the lasagna noodles according to package directions until al dente.
Drain, rinse with cold water, and toss with a little more oil to prevent sticking.
Sauté the Aromatics: Once the kale is cool enough to handle, squeeze out as much moisture as possible with your hands, then chop it finely.
In a large skillet, melt 2 tablespoons (30 ml / 1 fl oz) of butter over medium heat.
Add the minced garlic and onion and sauté for 5 minutes until softened.
Stir in the chopped kale and cook for another 5 minutes.
Make the Filling: Transfer the kale mixture to a large bowl.
Stir in the ricotta, mozzarella, ¼ cup of the Parmesan cheese, salt, and pepper until well combined.
Set aside.
Preheat your oven to 350°F / 175°C.
Create the Sauce: In a medium saucepan, melt 4 tablespoons (60 ml / 2 fl oz) of butter over medium heat.
Whisk in the flour and cook for 2 minutes, whisking constantly, to form a roux. Gradually whisk in the milk, followed by the tomato purée, nutmeg, salt, and pepper.
Continue whisking often until the sauce comes to a boil and thickens, about 5-7 minutes.
Remove from heat.
Assemble the Roll-Ups: Spread a thin layer of the tomato cream sauce on the bottom of a large baking dish. Lay one lasagna noodle on a flat surface and spread about ⅛ of the kale filling evenly over it.
Roll it up loosely and place it seam-side down in the prepared dish.
Repeat with the remaining noodles and filling.
Bake to Perfection: Pour the rest of the sauce evenly over the roll-ups.
Sprinkle with the remaining ¼ cup of Parmesan cheese.
Bake, uncovered, for 30 minutes, or until the sauce is hot and bubbly.
