Adjust rack to top position and preheat oven to 400 degrees. Wash and dry produce.

Quarter potatoes lengthwise, then slice into ¼-inch-thick pieces.

Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 10-12 minutes. Drain and set aside.

While potatoes cook, halve, peel, and thinly slice onion.

Heat a large drizzle of oil in a large, preferably nonstick, pan over medium-high heat. Add onion; cook, stirring occasionally, until browned and softened, 8-10 minutes.

Add spinach, Fry Seasoning, 1 tsp sugar (2 tsp for 12 servings) and a splash of water to pan with onion.

Cook until spinach is wilted and onion is caramelized, 2-3 minutes more.

Remove pan from heat. Stir in 1 TBSP butter (2 TBSP for 12) until melted; season with salt and pepper.

In a large bowl, whisk together sour cream, ¼ cup water, ¾ tsp salt, and pepper until well combined (½ cup water and 1½ tsp salt for 12 servings).

Whisk in eggs* until completely incorporated, 1-2 minutes. Wash and dry whisk (you’ll use it again in Step 6).

Stir in drained potatoes, spinach and onion mixture, and Italian cheese blend. (It’s OK if the veggies are still hot!)

Coat an 8-by-8-inch baking dish (9-by-13-inch baking dish for 12 servings) with nonstick cooking spray.

Pour egg mixture into prepared baking dish and evenly top with pepper jack.

Bake on top rack until eggs are set and cooked through and cheese is lightly browned, 20-25 minutes.

While frittata bakes, in a small bowl, whisk together sun-dried tomato paste and mayonnaise until smooth.

Cover with plastic wrap and refrigerate until ready to serve.

Let frittata cool for 5 minutes, then cut into 6 pieces (12 pieces for 12 servings).

To serve: Divide frittata between plates and serve with aioli on the side.

To stash: Let frittata cool completely. Refrigerate frittata and aioli in separate airtight containers for up to 3 days. Reheat in the microwave for 1-2 minutes.