Thinking outside the omelet—both sweet and savory.
In a large sauté pan, heat olive oil over high heat until shimmering. Add spinach and cook, tossing occasionally until spinach is dry but still bright green. Add chive and garlic and cook until chives are well wilted. Mixture should remain bright green. Transfer vegetables to a blender and set aside.
Use softened butter to grease 8 (6-ounce) soufflé dishes or ramekins. Coat the inside of each cup with grated Parmesan cheese. Place cups on a baking sheet.
Preheat oven to 375° F.
In a small bowl, combine flour, mustard and salt. Set aside.
In a small saucepan over medium heat, cook the butter until foamy. Add flour mixture, stirring over medium heat until completely combined and thickened. Cook for about 2 minutes. Do not brown.
Whisk in hot milk and increase heat to medium high. Bring to a boil and reduce heat to low.
In a small bowl, beat the egg yolks until creamy and opaque. Temper yolks into milk mixture, whisking constantly. Remove from heat and add cheese. Whisk well. Transfer soufflé base to blender and purée vegetables with base. Return base to saucepan and set aside.
In the bowl* of a stand mixer fitted with whip attachment, whip egg whites, water and cream of tartar until glossy and firm. Remove bowl from mixer. With a spatula, gently stir and fold in ⅓ of whites to soufflé base to lighten. Gently fold in the remaining whipped whites in 2 more additions.
Working quickly, overfill each soufflé dish and use a palette knife to level the tops. Use your thumb to wipe around the rim of each dish, making sure that no batter is clinging to the rim.
Place soufflés into preheated oven and bake for about 15 minutes until soufflés are raised, well puffed and lightly browned on the top. Remove from oven and serve immediately.
* The egg whites, bowl and whip attachment must be absolutely free of yolk and grease or the whites will not whip properly.
** If you don’t have superfine sugar in your pantry, don’t make an extra trip to the grocery. Simply place regular granulated sugar in the food processor or blender and blend until it is, well, super fine.