Heat your oven to 375°F and position your rack in the upper third. Grab a 10-inch oven-safe skillet and melt the butter over medium heat. Once it's foaming (not brown), toss in your diced onion and cook for about 2 minutes until it softens a tiny bit.

Add your sliced asparagus and spinach to the pan. Cook for 2-3 minutes, stirring occasionally, until the asparagus gets tender-crisp and the spinach wilts down. You'll notice the pan smells amazing at this point — that's the fresh herbs doing their thing.

Scatter your cherry tomatoes and peas across the veggies. Give everything a quick stir to distribute evenly. The tomatoes will start releasing their juices, which is perfect — that's extra flavor.

In a separate bowl, whisk together your 8 eggs and 1/2 cup milk until totally combined. Add salt, pepper, and that fresh dill. Whisk it real good so you don't get bits of separated egg white later.

Pour your egg mixture directly over the veggies in the skillet. Don't panic if it looks watery — it thickens up fast. Sprinkle your shredded cheese evenly across the top, making sure it covers most of the surface.

Cook on the stovetop for about 3-4 minutes until the edges start to set. You'll see the mixture pull away slightly from the sides. The center will still be jiggly — that's exactly what you want.

Transfer your skillet to the oven and bake for 18-22 minutes until a knife inserted in the center comes out clean. The top should be golden and puffed up like it just came from a fancy brunch spot. Let it cool for 2 minutes before slicing.