Rhubarb Custard Bars are my absolute favorite spring treat to make when those ruby-red stalks start popping up in my garden! These bars combine a buttery shortbread crust with a sweet-tart rhubarb custard filling that’s simply irresistible. I love how the tangy rhubarb balances perfectly with the creamy custard layer.

Ingredients Needed

For the crust:

1½ cups all-purpose flour
¾ cup cold butter, cubed
¼ cup powdered sugar

For the filling:

3 large eggs, lightly beaten
2 cups white sugar
½ cup all-purpose flour
½ teaspoon salt
4 cups rhubarb, diced

How to Make Rhubarb Custard Bars

First, I preheat my oven to 350°F and make sure to grease my 9×13 inch baking pan well.
For the crust, I combine 1½ cups flour and ¼ cup powdered sugar in a medium bowl. Then I grab my pastry blender (though two forks work in a pinch!) and cut in ¾ cup cold, cubed butter until everything looks like coarse crumbs.
I gently pat this crumbly mixture into my greased baking pan, making sure it’s evenly distributed.
Then I pop the crust into the oven for about 10-12 minutes, just until it gets a light golden brown color.

Make the Custard Filling

While my crust is baking, I prepare the filling by mixing together 3 lightly beaten eggs, 2 cups of white sugar, ½ cup flour, and ½ teaspoon salt in a large bowl.
Next comes the star ingredient – I gently fold in 4 cups of diced rhubarb. I try not to stir too vigorously so my rhubarb pieces stay intact.
When the crust comes out of the oven (still hot!), I immediately pour my rhubarb custard mixture over it.
I return the pan to the oven, reduce the temperature to 325°F, and bake for another 30-35 minutes. I know it’s done when the filling is set and doesn’t jiggle when I gently shake the pan.

Make the Frosting

Although the original recipe doesn’t include frosting, I sometimes like to add a simple cream cheese topping to make these bars extra special:

I blend 8 ounces of softened cream cheese with ½ cup softened butter and 2 cups powdered sugar.
Then I mix in 1 teaspoon of vanilla extract and spread this over the completely cooled bars.
If I’m feeling fancy, I sometimes garnish with thin slices of fresh rhubarb or a light dusting of powdered sugar.

How to Store Rhubarb Custard Bars

These bars need to be refrigerated because of the custard filling. After they’ve cooled for about 30 minutes on the counter, I cover the pan with plastic wrap and pop it in the fridge for at least 2 hours (though overnight is even better!). They’ll keep nicely refrigerated for up to 5 days, though they rarely last that long in my house!

If I want to freeze some, I cut them into individual servings, wrap each one in plastic wrap and then foil, and freeze for up to 3 months. I just thaw them overnight in the refrigerator when I’m ready to indulge.

Recipe Notes

When selecting rhubarb, I look for firm, crisp stalks with a bright color. The redder the stalks, the sweeter they tend to be!
I’ve found that cutting the rhubarb into small, uniform pieces (about ½ inch) helps it cook evenly and makes the bars easier to cut.
If my rhubarb is particularly tart, I sometimes add an extra ¼ cup of sugar to the filling.
For the best texture, I make sure not to overbake the bars – once the custard is set but still has a slight jiggle (like Jell-O), it’s ready!
I always let these bars chill completely before cutting them. A chilled bar cuts much more cleanly than a warm one.

Frequently Asked Questions

Can I use frozen rhubarb for these bars?
Absolutely! I’ve made these with frozen rhubarb many times. I just make sure to thaw it completely and drain off any excess liquid before adding it to the custard mixture.

The bars seem too sweet/tart for my taste. What can I adjust?
If you find the bars too sweet, I’d reduce the sugar to 1½ cups. If they’re too tart, consider adding an extra ¼ to ½ cup of sugar to the filling.

Can I add strawberries to this recipe?
Yes! I sometimes swap out 1 cup of the rhubarb for fresh strawberries. The combination is delicious and makes for a beautiful color contrast.