Set the Multi-Function Cooker to Sauté/Sear Mode, MEDIUM. Press Start.
Melt butter in the Multi-Function Cooker. Add onions and cook, stirring occasionally until onions are caramelized, about 15-20 minutes. Add mushrooms, bell pepper and garlic. Cook, stirring occasionally, until vegetables are tender. Add flour and salt. Cook for 1 minute, stirring constantly. Gradually add cream, half-and-half and nutmeg and cook until slightly thickened. Gradually stir in Gruyère cheese until melted. Add kale to the Multi-Function Cooker in batches, letting each batch wilt before adding additional kale, and stirring until combined. Cover and set the Multi-Function Cooker to Manual Mode, LOW for 2 hours. Press Start.
Preheat oven to 400°F (200°C). In a small bowl, stir together panko, Parmesan and melted butter. Remove vessel from the Multi-Function Cooker and uncover. Sprinkle bread crumb mixture over kale mixture.
Bake uncovered in oven until bread crumbs are golden brown, about 15 minutes.
Variation: Squash and Zucchini Casserole
Make as directed, omitting mushrooms and kale. Substitute 2 pounds (908 grams) each of zucchini and yellow squash. Remove caramelized onions from Multi-Function Cooker. Set aside. Add 1 tablespoon (15 milliliters) olive oil. Sauté zucchini and yellow squash in two batches until barely fork tender. After removing from Multi-Function Cooker, place squash in colander and sprinkle with 2 teaspoons (6 grams) kosher salt. Let drain while finishing recipe preparation, then pat dry. Add additional olive oil if necessary to Multi-Function Cooker. Sauté bell pepper and garlic until tender, 1-2 minutes. Make the sauce by increasing flour to ½ cup (63 grams), adding 1 teaspoon (3 grams) kosher salt and substituting 2 cups (150 grams) shredded extra-sharp Cheddar cheese for Gruyère and ¼ teaspoon crushed red pepper for nutmeg. Return squash and onions to the Multi-Function Cooker and stir until combined. Cover and cook as directed.
Variation: Scalloped Potatoes
Make as directed, omitting mushrooms, bell pepper, garlic and kale. In the Multi-Function Cooker vessel, bring 4 pounds (1812 grams) thinly sliced Yukon gold potatoes, 1 tablespoon (9 grams) kosher salt and water to cover to a boil over medium-high heat on stovetop. Cook until barely tender, about 10 minutes. Drain well. Set the Multi-Function Cooker to Sauté/Sear Mode, MEDIUM. Press Start. Add 3 cups (450 grams) chopped sweet onion in place of 2 medium onions and add ¼ cup (57 grams) unsalted butter. Cook, stirring occasionally, until caramelized, 10-15 minutes. Remove onions. Make sauce by substituting 1½ cups (150 grams) fontina cheese for Gruyère and ½ teaspoon (1 gram) white pepper for nutmeg. Add garlic and 2 teaspoons (6 grams) kosher salt. Return potatoes and onion to the Multi-Function Cooker and stir until combined. Cover and cook as directed.