Step 1

Position a rack in the middle of the oven and preheat to 375 degrees. Brush a 12-well nonstick muffin pan with oil.

Step 2

In a large skillet over medium heat, heat 1 tablespoon of oil until shimmering. Add the onion and cook, stirring occasionally, until just softened, about 3 minutes. Add the frozen vegetables and cook, stirring occasionally, until just thawed, 2 to 3 minutes. Remove from the heat and let cool for 15 minutes.

Step 3

In a medium bowl, whisk together the eggs and milk. Stir in 1/4 cup (1 ounce) of the cheese, the vegetables, salt and pepper.

Step 4

Distribute the mixture evenly among the muffin pan cups, filling each about three-quarters of the way. Top with the remaining 1/4 cup (1 ounce) of cheese. Bake for 18 to 20 minutes, or until set in the center. Let rest in the pan for 5 minutes before removing; you may need to run a butter knife or offset spatula around the edges if they don’t slide out easily. Serve warm or let cool completely.