- 2 oz unsalted butter Cold
- 1/2 cup brown sugar Packed
- 1/2 cup all-purpose flour
- 1 cup walnuts Roasted and chopped
- 1/4 tsp kosher salt
- 4 oz unsalted butter Room temperature
- 1/2 cup brown sugar Packed
- 1 1/4 cups all-purpose flour
- 1 tsp vanilla extract
- 1 tsp almond extract
- 3/4 cup walnuts Roasted and chopped. Pecans work too.
- 1/4 tsp kosher salt
- 2 lb Italian prune plums About 24. Halved and pitted. Pink or amber flesh bakes sweeter than green.
- 1/2 cup cornstarch
- 1 cup brown sugar Packed
- 1 Tbsp vanilla extract
-
Mix the crumble.
In a food processor: pulse 2 oz unsalted butter, 1/2 cup brown sugar, 1/2 cup all-purpose flour and 1/4 tsp kosher salt until it clumps.
By hand: rub the same four together with your fingertips. Either way, stop when it holds together in chunks, then mix in 1 cup walnuts, roasted and chopped. -
Freeze it. Put the bowl in the freezer and leave it there until you assemble. Cold crumble keeps its clumps in the oven.
-
Cream the butter and sugar. Beat 4 oz unsalted butter, at room temperature, with 1/2 cup brown sugar until smooth.
-
Add the flour and extracts. Mix in 1 1/4 cups all-purpose flour, 1 tsp vanilla extract, 1 tsp almond extract and 1/4 tsp kosher salt until it comes together into a chunky dough. Mix in 3/4 cup walnuts, roasted and chopped, and set it aside.
-
Heat the oven and line the pan. Preheat to 350°F. Line an 9x9 inch pan with parchment that comes about 2 inches up the sides, so the whole slab lifts out later.
-
Coat the plums in cornstarch. Halve and pit 2 lb Italian prune plums, then toss them with 1/2 cup cornstarch until every cut side is coated.
-
Add the sugar and vanilla. Fold in 1 cup brown sugar and 1 Tbsp vanilla extract. Do this right before you assemble so the sugar has no time to pull the juice out.
-
Press in the base, and up the sides. Spread the shortbread over the bottom of the lined pan, press it down firmly and evenly, then bring it up the sides about 1 1/2 inches. The flat bottom of a measuring cup does this well. That wall holds the plum juices in while the bars set.
-
Layer the plums. Arrange the halves over the crust cut side up, packed tight. Do not shake the pan to settle them - it can loosen the crust you just pressed in. Scrape whatever sugar and cornstarch is left in the bowl out over the fruit.
-
Top with the frozen crumble. Break it into chunks over the plums. If it looks like sand, press handfuls together in your palm first, then break those over the top.
-
Bake about 1 hour 20 minutes. The top should be deep golden, the center should be bubbling, and a thermometer in the middle should read 200°F to 205°F. If you take it out before the center bubbles, the juices stay thin and the cornstarch never thickens them.
-
Cool before cutting. Warm from the oven it is a spoon-and-ice-cream dessert. For clean squares, cool it completely, lift the slab out by the parchment and cut it on a board.
Recipe Video
- Pan: a 9" x 9" pan, the one in the photos. Other pans work. A wider pan spreads the bars thinner and they bake faster, so follow the temperature cue below rather than the clock.
- Plums - check the flesh color: cut one open before you bake. Pink or amber flesh bakes mellow and sweet. Green flesh bakes tart, because the oven drives off water and concentrates the acid. Both can be fully ripe, so go by color, not ripeness. With green-fleshed plums, add a little extra sugar to the fruit.
- Plum variety: Italian prune plums (small, oval, deep blue) hold their shape and are not too wet. Regular red or black plums work; cut them into quarters and let them drain in a sieve for 10 minutes after mixing with the sugar.
- Doneness: 200°F to 205°F in the center is the cue that matters. The cornstarch needs that heat to set, and the top browns before the middle gets there.
- Yield: about 4 lb (1.85 kg) baked. Cut 3 across and 4 down for 12 bars of roughly 5.4 oz (155 g) each.
- Make it ahead: the crumble keeps in the freezer for up to a month, so you can make it well in advance.