Grandma’s Rhubarb Crumb Bars

Grandma’s Rhubarb Crumb Bars are the kind of recipe that just feels like home. You know the ones- mismatched mugs in the cupboard, the hum of the old fridge, and something cooling on the counter that you weren’t supposed to touch yet!

Grandma’s Rhubarb Crumb Bars

These tart, buttery rhubarb crumb bars are just sweet enough to keep you coming back for one more bite. They’re equally perfect with a scoop of vanilla ice cream or served up next to scrambled eggs and sausage. Yep – I said breakfast. If coffee cake counts in the morning, these do too.

Gather Your Ingredients

These bars come together with ingredients you probably already have on hand, minus maybe the rhubarb (and if that’s the case, add it to your next farmer market run or raid a neighbor’s patch – rhubarb people are usually generous).

For the rhubarb filling:

• 3 cups rhubarb, chopped
• 1 1/2 cups granulated sugar
• 3 Tablespoons corn starch
• 1/2 cup cold water
• 1 teaspoon vanilla extract
• 3 Tablespoons strawberry jam (optional, but you’ll regret skipping it)

For the oat crumble:

• 1 1/2 cups oatmeal (quick-cook or old-fashioned both work)
• 1 1/2 cups all-purpose flour
• 1 cup packed brown sugar
• 1 cup cold butter, cubed

Let’s Make Grandma’s Rhubarb Crumb Bars

First things first, preheat that oven to 350 degrees and lightly grease a 9×13 baking dish. Then let’s get cooking – literally.

Step 1: Cook the Rhubarb Filling

Grab a medium saucepan and toss in your chopped rhubarb, sugar, cornstarch, cold water, and vanilla. Set it over medium heat and stir occasionally while it cooks down and thickens. This usually takes about 8 minutes.
You’ll know it’s ready when the liquid has turned glossy and the mixture has a consistency similar to pie filling. Remove it from the heat and set it aside to cool slightly. And yes, it already smells amazing.

Step 2: Mix the Crumble

In a large mixing bowl, combine your oatmeal, flour, and brown sugar. Cut in the cold butter using a pastry cutter or fork until you’ve got a coarse crumb texture. Some pieces will be bigger than others – that’s totally fine.
This is the same mixture used for both the base and the topping. Fewer dishes. More crumble. We love a win-win.

Step 3: Build the Bars

Take about 3/4 of your crumble mixture and press it into the bottom of your prepared baking dish. You want a firm, even layer- it’s what holds everything together.
Then pour your rhubarb mixture over that base and spread it out gently.
If you’re using strawberry jam (please do), heat it for about 15 seconds in the microwave until pourable. Drizzle it over the rhubarb layer and then run a butter knife through it to swirl. This step adds a little extra sweetness and pairs beautifully with the tart thubarb.
Now take the remaining crumble and scatter it over the top. Don’t worry about making it perfect- some of the filling peeking through adds to the charm and rustic farmhouse look.

Step 4: Bake

Bake in the preheated oven for 30-35 minutes, or until the top is golden brown and your house smells like your childhood. Let the bars cool completely before slicing (if you can wait that long).

Tips, Tricks, and Questions Answered

Can I use frozen rhubarb?
Absolutely. Just measure it straight from frozen and maybe add an extra minute or two when cooking down the filling.

Do I have to use strawberry jam?
Nope. But should you? YES. It gives the tart rhubarb a sweet companion and adds a subtle fruity twist that people can’t quite put their finger on – but they’ll ask for the recipe, guaranteed.

Can I use quick oats or old-fashioned oats?
Either works. Old-fashioned will give you a chewier texture, while quick oats blend in a little more. Don’t use instant oats, though – they’re too powdery for coarser more textured crumble.

Can I make these gluten-free?
Yes! Just use a good 1 to 1 gluten-free flour and certified gluten-free oats. The texture may be a little different, but still delicious.

How do I store them?
Once cooled, store in an airtight container on the counter for up to 3 days or in the fridge for up to 5. They freeze great, too – just slice, wrap in parchment, and freeze in a zip-top bag.

Are they really good for breakfast?
Okay, look – I’m not saying these are health food, but I am saying they pair perfectly with a plate of scrambled eggs and cripsy bacon. It’s the sweet savory balance we all secretly love. And honestly, if Pop-Tarts get a breakfast pass, so do these.

Can I double the recipe?
Yes – but you’ll nee a second pan. These bars are thick and need room to bake evenly, so avoid trying to put a double batch into one dish.

How do I get clean slices?
Let them cool completely before cutting, and use a sharp knife wiped clean between cuts. Or embrace the messy edge pieces – they’re the best ones anyway.

Whether you serve them at a church potluck, sneak a square with you morning coffee, or plate them up next to a hot breakfast skillet, Grandma’s Rhubarb Crumb Bars are the kind of comfort food that always feels right.

More Rhubarb Recipes

My friends over at These Old Cookbooks have a mile-long list of amazing recipes using rhubarb! This Old Fashioned Rhubarb Coffee Cake looks terrific, and this Strawberry Rhubarb Jam with Jello is definitely on my list to make before I run out of fresh rhubarb!

These are called bars – the longer they cool, the easier it is to cut them into bars and have them hold their shape. But let’s be real there are times that one cannot be that patient and shouldn’t have to be. Scoop some of it warm out of the pan and add some ice cream. Enjoy them as you want, don’t be bound by rules.