Mom’s Thrifty Potato Casserole

Old-fashioned potato casserole layered with peas, onions, cheddar cheese, and homemade cream of mushroom sauce. 

 Buying condensed soups isn’t as budget-friendly as it once was, and my mom knew that long before it became common conversation. When she was short on time, she’d reach for a store-bought can—but when she had a few extra minutes, she made her own cream of mushroom soup from scratch. It was simple, hearty, and full of flavor.

This casserole-style dish is one of those comforting meals that fed a family well without fuss. Thinly sliced potatoes, onions, peas, and cheese come together with a creamy mushroom base to create a warm, satisfying supper—proof that homemade doesn’t have to be complicated to be delicious.

Ingredients:  

1 onion, cut in half and thinly sliced
5–6 potatoes, peeled and thinly sliced
1/2 tsp. salt
1 package (10 ounces) frozen peas
2 c. shredded sharp cheddar cheese, divided
1/4 c. butter
1 (8-ounce) can mushrooms, drained and finely chopped
1/3 c. flour
1/2 tsp. garlic powder
1/4 tsp. onion powder
1/4 tsp. black pepper
1/4 tsp. salt
1 cup chicken broth
1 cup milk

Directions:

Preheat the oven to 350°F. Lightly grease a 9 × 13-inch casserole dish or similar 3-quart baking dish.

In a medium saucepan over medium-low heat, melt the butter. Add the chopped mushrooms, garlic powder, onion powder, pepper, and salt. Cook for 2–3 minutes, stirring occasionally, until fragrant.

Sprinkle the flour over the mushroom mixture and stir well to combine. Cook for about 1 minute to remove the raw flour taste.

Slowly pour in the chicken broth while stirring constantly to prevent lumps. Gradually add the milk, continuing to stir until smooth.

Bring the mixture to a gentle simmer and cook for 2–3 minutes, stirring often, until the sauce thickens to a creamy consistency. Remove from heat and set aside.

Layer one-fourth of the sliced potatoes in the bottom of the prepared baking dish. Top with one-fourth of the sliced onions and sprinkle lightly with salt and pepper. Scatter one-fourth of the frozen peas over the top.

Spoon one-fourth of the mushroom sauce evenly over the vegetables and sprinkle with 1/2 cup of the shredded cheddar cheese.

Repeat the layers three more times, finishing with the remaining cheese on top.

Cover the dish with a lid or foil and bake for 45–50 minutes, or until the potatoes are tender.

Remove the foil and continue baking for another 10–15 minutes, until the casserole is bubbly and lightly golden on top.

Allow the casserole to rest for about 5 minutes before serving.

Tips for Best Success:

• Slice the potatoes thin and evenly so they cook at the same rate.
• If the potatoes are sliced thicker, the casserole may need an additional 10 minutes of baking time.
• Stir the sauce constantly when adding the broth and milk to keep it smooth and lump-free.
• Let the casserole rest briefly after baking so the sauce thickens slightly before serving.

Variations and Substitutions:

• Ham or bacon can be added for a heartier casserole.
• Cheddar cheese can be replaced with Monterey Jack, Colby, or a cheese blend.
• Fresh mushrooms can be used instead of canned if desired.
• Add cooked ground beef or diced chicken to turn this into a complete meal.
• Frozen mixed vegetables can be used instead of peas.

 Serving Suggestions:

This casserole pairs well with roasted chicken, baked pork chops, or meatloaf.

Serve it alongside a crisp green salad or steamed green beans for balance.

It also works well as a hearty vegetarian main dish with warm dinner rolls on the side.

How to Store:

Refrigerator:
Store leftovers in an airtight container in the refrigerator for up to 4 days.

Reheating:
Reheat individual portions in the microwave or warm the casserole in a 325°F oven until heated through.

Freezer:
This casserole can also be frozen for up to 2 months. Thaw overnight in the refrigerator before reheating.

Frequently Asked Questions:

Can I use fresh mushrooms instead of canned?
Yes. Use about 1 cup of finely chopped fresh mushrooms and sauté them in the butter until softened.

Can I make this casserole ahead of time?
Yes. Assemble the casserole, cover, and refrigerate for up to 24 hours before baking.

Do I need to thaw the peas first?
No. Frozen peas can be added directly to the casserole.

What potatoes work best?
Russet or Yukon Gold potatoes both work well for this dish.

Why are my potatoes still firm?
They may have been sliced too thick. Thin slices cook more evenly and absorb the sauce better.