Preheat oven to 375 degrees F. Chop the fresh herbs and artichoke salad.: You'll notice a warm, dry heat build in the oven that ensures even cooking, creating a gently puffed top and set center. Preheating matters because placing the dish into a fully heated environment promotes consistent rising and browning; otherwise the edges may overcook before the center firms. A common mistake is under preheating, which can lengthen bake time and lead to a soggy middle. When the oven reaches temperature, it should feel uniformly hot when you briefly hold your hand near the closed door, not blistering but noticeably warm.
Set a skillet over medium heat and add 1 tablespoon olive oil. Sauté the spinach and garlic until wilted, about 3 minutes.: Freshly chopping releases the aromas of the dill and breaks the artichoke salad into bite sized pieces that distribute evenly. The scent will be herbaceous and slightly briny from the artichoke and olive components, signaling freshness. Finely chopping helps prevent large pockets that could cause an uneven texture in the casserole. Avoid leaving pieces too large, which can concentrate wetness and create dense spots.
Oil a 9×13 inch baking dish and layer the spinach and artichoke salad evenly in the dish.: As the oil warms, it will shimmer slightly, releasing a soft fruity perfume from the oil. This gentle heat prepares the pan to quickly wilt the spinach and bloom the minced garlic flavor. If your pan is too hot, the garlic can brown too fast and taste bitter, so aim for a medium heat where you'll hear a light sizzle but not vigorous spattering.
In a medium bowl, whisk together the eggs, milk, herbs, salt and lemon pepper.: The sound will change from a pronounced sizzle to a softer, steady whisper as the leaves release moisture. Visually, the spinach will collapse and turn glossy deep green, while the garlic turns translucent. This step concentrates the green flavor and removes excess water that could make the casserole runny. Overcooking until the leaves are dry and brown is the usual mistake, so remove from heat while still tender and moist.
Pour the egg mixture over vegetables and sprinkle with feta cheese. Bake in the center of the oven for 35-40 minutes until firm in the center.: Coating the dish helps prevent sticking and promotes gentle browning at the edges. Layering the wilted spinach first and then the chopped artichoke salad ensures an even distribution of textures. As you spread the mixture, you should see a mosaic of green and briny bits. If you skip oiling, bits can cling and overbrown, making cleaning harder and affecting presentation.
In a medium bowl, whisk together the eggs, milk, herbs, salt and lemon pepper: As you whisk, the mixture becomes homogenous and slightly glossy, smelling faintly of herb and citrus from the lemon pepper. The milk lightens the eggs and creates a silky custard once baked. Whisk just until combined to avoid adding too much air which could produce large holes in the finished casserole. A common misstep is overwhisking, resulting in an airy texture rather than a smooth set.
Pour the egg mixture over vegetables and sprinkle with feta cheese: When poured, the custard will settle and seep into crevices, coating the spinach and artichoke pieces. The crumbled feta on top will show as white islands that soften and slightly melt, releasing salty, tangy pockets of flavor. Ensure an even pour to avoid clumps of custard in certain spots. If the dish looks overly wet, it often evens out during baking, but be mindful of excess liquid from under drained artichoke salad.
Bake in the center of the oven for 35 to 40 minutes until firm in the center: During baking you will see the edges take on a faint golden color and the middle will set, changing from glossy to matte. A gentle jiggle should show only minimal movement when it is done, and a toothpick inserted near the center will come out mostly clean. The aroma will be savory and herby with a hint of browned cheese. Pulling it out too early yields a runny center, while overbaking leads to dryness, so aim for that tender set described above.
