Preheat your oven to 400 degrees. This ensures that the casserole bakes evenly and gets that perfect golden crust on top.
Take out an 11” oven-safe casserole dish and lightly grease the bottom with butter or cooking spray. This will help prevent sticking and make for easier cleanup.
Now, it’s time to prep the potatoes. Using a mandoline slicer, slice your yellow potatoes thinly, about ¼” thick. The thinner they are, the faster they'll cook and the creamier the final product will be.
Layer half of the sliced potatoes at the bottom of your casserole dish. You can get creative here! Feel free to mix and match yellow potatoes and sweet potatoes for added color and flavor.
Next, add a layer of half the mixed frozen vegetables, spreading them evenly over the potatoes. This adds a nice texture and flavor to your dish.
Now, add the rest of the sliced potatoes on top of the vegetables. Make sure not to overfill the dish, as everything will expand while baking.
Next, add another layer of the remaining mixed frozen vegetables to top it off.
In a mixing bowl, whisk together the milk, flour, and pesto. This mixture will create a creamy sauce that seeps down into the layers of potatoes and vegetables.
Pour the pesto milk mixture over the layers in your casserole dish, ensuring everything is coated without overflowing.
Finally, sprinkle the freshly grated cheddar cheese generously over the top. This will create a deliciously cheesy crust as it bakes.
Cover the casserole with foil and place it in the preheated oven. Bake for 30 minutes, then remove the foil and bake for an additional 20-30 minutes. You’ll know it’s ready when the potatoes are tender and can be easily pierced with a fork.
