1-First Step: Get the oven and pan ready Start by preheating your oven to 375 degrees Fahrenheit. Then grease a 9×9 or equivalent oven-proof pan so the casserole does not stick. This small step matters more than it sounds, especially with a cheesy zucchini gratin that bakes into soft, melty layers. While the oven heats, slice the zucchini and onion thinly. Aim for about 1/4 inch thick slices so everything cooks at the same pace. Thin slices help the vegetables soften fully and keep the low carb casserole from turning watery or uneven.

2-Second Step: Build the first layer Overlap one-third of the zucchini and onion slices in the prepared pan. Think of it like making neat little vegetable shingles. It does not have to be perfect, but the more evenly you layer, the better the final bake will look. Season that first layer with salt and pepper to taste, then sprinkle on 0.5 cup of the shredded pepper jack cheese. That first cheese layer helps hold the vegetables together and starts building the rich flavor that makes this keto zucchini dish so satisfying.

3-Third Step: Repeat the layers Repeat the same process two more times until all the zucchini, onions, and cheese are used up. Each layer should get a little salt and pepper, then another sprinkle of cheese. This layering method gives the casserole that classic au gratin casserole look and helps every bite taste balanced.

4-Fourth Step: Make the creamy sauce Now grab a microwave-safe dish and combine 0.5 teaspoon garlic powder, 2 tablespoons butter, 0.5 cup heavy whipping cream, and 0.25 teaspoon xanthan gum. Microwave for one minute, just until the butter melts. Then whisk until smooth.

5-Fifth Step: Pour and bake Pour the creamy mixture evenly over the layered zucchini and onion. Try to distribute it across the whole pan so the sauce sinks into the vegetables instead of sitting in one spot. This is where the whole thing starts looking like real comfort food. Bake at 375 degrees Fahrenheit for about 45 minutes, or until the casserole is thickened and golden brown on top. The edges should look bubbly, and the center should be set. Your kitchen will smell amazing, and honestly, that is half the reward.

6-Final Step: Serve warm Once it comes out of the oven, let it rest for a few minutes before serving. That short wait helps the sauce settle, which makes scooping easier. Serve warm as a side dish with chicken, steak, pork chops, or even a simple salad.