Soufflés have a rep for being super fussy and difficult, but once you make one, you'll think, "Really? That's it?" The most important thing to remember is that temperature consistency is key, so don't open the oven door until the soufflé is done (if you need to peek, use the oven light). These individual soufflés are fantastic for brunch but also would work for dinner.
Place a rack in the lowest position of the oven and preheat the oven to 375ºF.
Melt 1 Tablespoon of the butter and brush it all over the insides of four 8-ounce ramekins. Divide the Parmesan evenly among the ramekins and swirl it around until the cheese coats the bottoms and sides. use a paper towel to wipe off the rims. Refrigerate the ramekins.
In a medium saucepan, melt the remaining 2 tablespoons of butter over medium heat. Add the cassava flour, season with a pinch of salt, and whisk until a paste forms. Cook, whisking constantly, until the paste turns light golden, about 30 seconds. Slowly drizzle in the half-and-half, whisking constantly and vigorously, until the mixture is smooth. Reduce the heat to low and cook, stirring and scraping the bottom, sides, and corners of the pan, until the sauce has thickened, about 1 minute (don't let it boil). Remove the pan from the heat and whisk in the cheddar, Pluck, cayenne, and chives. Whisk until the cheese melts (if it doesn't, place over the lowest heat and whisk until smooth). Taste and season generously with salt and pepper, if desired. Transfer to a large bowl.
Separate the eggs, placing the yolks in a medium bowl and the whites in a clean, dry large mixing bowl. Whisking vigorously, drizzle a few tablespoons of the cheese sauce into the yolks. Drizzle the yolk mixture back into the sauce, whisking continuously.
Using a clean, dry whisk or electric mixer on high speed, beat the whites until they turn foamy. Add the cream of tartar and continue to beat until firm peaks form, 2 to 3 minutes longer.
Using a silicone spatula, fold one-fourth of the whites into the yolk mixture. Fold in the remaining whites just until incorporated.
Place the ramekins on a rimmed baking sheet. Divide the mixture among the ramekins, filling them about three-quarters full. Bake until the soufflés are puffed and golden, 20-23 minutes. Serve immediately.