Step 1

Preheat oven to 350°F

Step 2

In your large mixing bowl, prepare an ice bath (water and ice).

Step 3

In a large pot of salted boiling water, add green beans and cook until bright green and crisp tender, about 2-4 minutes. If doubling the recipe, boil in batches.

Step 4

Use a slotted spoon to transfer the green beans to the prepared ice bath to cool for about 4 minutes.

Step 5

When well cooled, move green beans to a towel to drain, then into to a casserole dish.

Step 6

Heat oil in a non-stick pan over medium-high heat.

Step 7

Sautée onions until translucent, then add garlic and mushrooms. Cook for an additional 5 minutes

Step 8

Season with salt and pepper and add to the casserole dish, mixing with the green beans.

Step 9

In a saucepan, whisk milk, cornstarch, and a pinch of salt and pepper.

Step 10

Bring to a boil, then stir in ½ cup grated cheese.

Step 11

Continue to simmer for a couple of minutes until the sauce thickens and the cheese is melted.

Step 12

Remove from heat and pour cheese mixture over the vegetables. Toss until well coated.

Step 13

In a small mixing bowl, combine panko with remaining ¼ cup of cheese and sprinkle onto the casserole.

Step 14

Bake at 350°F until bubbly and golden on top, about 25-30 minutes.