How to Make It
Preheat the oven to 375°. Line a baking sheet with parchment and arrange flatbread rounds.
Rinse the kale and add the leaves to a pot with 2 tablespoons of water over medium heat. Cover and cook until kale is tender, about 6 minutes. Squeeze excess water from the kale, and transfer to cutting board to finely mince, add to a small bowl and set aside.
Combine the milk and heavy cream in a small saucepot over low to medium heat and bring to a simmer. Meanwhile, in a separate saucepot over medium heat, melt the butter until it begins to froth. Add the flour to the butter and cook, stirring constantly, until the roux turns a pale yellow colored paste. Using a wire whisk, slowly add the warm milk mixture to the butter roux, whisking vigorously to avoid lumps.
Add the garlic, onion, and salt to the pot and simmer for 15 minutes until the cream base is fragrant. The sauce should be just thick enough to coat the back of a spoon. Stir in 1/3 cup of the chopped kale until incorporated. If consistency is too thick, add a touch of milk to loosen. Season to taste with salt and black pepper.
Spread a generous layer of the sauce over the flatbreads, top with cheeses, a few artichoke hearts, and bake for 15-20 minutes until cheese has melted and sauce bubbles off the sides a bit. Cut into strips and serve.