Bring a pot of salted water to a boil. Add cauliflower florets and simmer for 4–5 minutes until just tender. Drain well.
Make the Egg Mixture
In a large bowl, whisk together eggs, crème fraîche, mustard, and paprika until smooth.
Stir in chopped chives, most of the grated cheese (reserve a handful), and season with salt and pepper.
Cook the Frittata
Preheat oven to 375°F.
Heat olive oil in a large oven-safe skillet over medium-high heat. Add cauliflower and cook undisturbed for 5–6 minutes, until golden on one side.
Pour in the egg mixture, gently shaking the pan or using a spatula to distribute the cauliflower evenly.
Cook on the stovetop for 5 minutes until the edges begin to set.
Sprinkle remaining cheese over the top and transfer the pan to the oven.
Bake for 12–15 minutes, or until puffed, golden, and fully set.
Let rest for 5 minutes before slicing. Serve warm or room temp.
Notes
Storage: keeps well in an airtight container in the fridge for 3-4 days, good cold, at room temp, or reheated gently in the oven or microwave. It's an easy one to make ahead for the week.