Plum Crumble Bars aka "The PLUMBLE"

This recipe began as something called Prune Plum Tart—a simple French recipe I’d inherited from a relative. I loved it even then, but each September I’d find myself jotting little notes in the margins: try brown sugar in the crumble instead of white, add an egg yolk to the crust for more structure, increase the salt. It’s turned into the slowest recipe development project of all time—because the bars were always delicious, the season for Italian prune plums is short, and the recipe was just for me, anyway.

Over the years, the tweaks piled up. The crust became (a little bit) sturdier, the crumble more layered, the fruit juices sweetened and thickened. Last year, friends insisted I stop adjusting. “It’s perfect,” they told me. And maybe it is—but tinkering has become part of the tradition. This year’s change? Swapping toasted walnuts for almonds—their softer texture and faintly bitter edge work better in the crumble—and increasing the quantity slightly, because why hold back?

The one constant in the recipe has been the fruit. These bars are designed to let the plums shine, with just enough spice in the topping to add warmth and complexity without pulling focus. I use Burlap & Barrel cinnamon and cardamom, both so vibrant that a little goes a long way. If your spices are more basic, you may want to increase the amounts—but I’ve made a note to try pushing the spicing further next time. If you do it first, let me know how it turns out.

Whichever path you take, the result is jammy, buttery, and worth the wait—like a pie distilled into its most essential parts. A couple of tips: the crust—essentially a sablé—will soften quickly if the fruit is wet, so if your fruit is especially juicy, increase the tapioca slightly. And always bake until the juices at the centre are thickened and syrupy; that’s when you know they’ll set properly and give you bars that slice neatly and last a little longer.

Here’s the latest version of the Plumble. This year I’ve added weights to the ingredient list, since that’s how I bake now, and it always gives a more accurate result. Try it as written, or if you make it your own, share your notes and questions so they can become part of the ongoing recipe, too.

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Plum Crumble Bars aka “The Plumble”

Makes 16 squares

Crust
½ cup (113 g) unsalted butter, cut into pieces
1 cup (135 g) all-purpose flour
3 tbsp granulated sugar
½ tsp Diamond Crystal kosher salt
1 egg yolk

Filling
454 g small firm-ripe blue prune plums (about 15)
3 tbsp (36 g) granulated sugar
4 tsp tapioca starch

Topping
3 tbsp (38 g) light brown sugar
¼ cup (34 g) all-purpose flour
2 tbsp (30 g) unsalted butter
¼ tsp Diamond Crystal kosher salt
¼ tsp Burlap & Barrel Royal cinnamon
¼ tsp Burlap & Barrel Cloud Forest cardamom
3 tbsp (20 g) finely chopped toasted walnuts

Method

1. Preheat oven to 350°F. Line an 8-inch square pan with parchment paper.

2. Combine butter, flour, sugar, and salt in a food processor or bowl. Pulse or rub with fingers until butter is the size of peas. Add egg yolk and mix until dough just starts to clump. Press evenly into prepared pan. Bake 22–25 minutes, until lightly golden all over. Cool slightly.

3. Halve plums lengthwise and remove pits (if you have larger plums you can quarter them). Toss with sugar and tapioca; let sit 20 minutes until juicy and all powdery bits are moistened.

4. For the topping, combine brown sugar, flour, butter, salt, cinnamon, and cardamom until crumbly. Add walnuts, squeezing crumble with your fingers to get a mix of big and small pieces.

5. Lay plums evenly over crust (a checkerboard of plums skin side up and down fits neatly if you like a pattern). Scrape any juices over top. Sprinkle with topping. Bake 1 hour to 1 hour 10 minutes, or until plum juices have bubbled and thickened and the topping is golden. Cool before cutting into squares.

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This recipe always feels like the true start of baking season. It feels good to turn the oven on again, and to fill the house with the scent of butter, fruit, and spice. Fresh, vibrant spices make all the difference here—Flavourfull’s collection from Burlap & Barrel, Diaspora Co, and Épices de Cru are the kind you’ll truly taste in every bite.

[Stock up for fall baking →]