A tart solution for sweet crumb cake
With easy-to-peel satsumas, seedless clementines and scarlet blood oranges all available to satisfy citrus yearnings, it can be hard to remember to give grapefruits their due.
Even when I do think to buy them, they often languish. Their vast size requires you either to commit or to share, and they’re not the kind of thing you’d casually toss into your bag on the way out the door. Grapefruits can also be somewhat bitter, which may turn off people accustomed to honey-sweet tangerines.
But dessert is different. That’s when the acidity and bitterness of grapefruit is precisely what makes it so appealing, especially in confections that lean cloying. Like crumb cake.
With its mound of brown sugar nuggets blanketing a moist, sour cream-enriched cake, crumb cake often walks the line between luxury and overkill. But adding grapefruit segments on top of the batter pulls it back from the sugary abyss, each bite releasing a burst of bracing, tangy juice.
Before adding the fruit segments, you have to remove the membranes that surround them, which interfere with flavour and texture. (This technique is known as supreming the fruit.) Once the membranes are removed, the segments will fall apart, and that’s perfectly fine. You’re aiming for a scattering of the pulp, each tiny juice vesicle remaining distinct until it hits your teeth.
I also sprinkle a few grains of sea salt on top of the grapefruit. It does wonders to mitigate the fruit’s inherent bitterness. But be restrained: you don’t want it to go the way of salted caramel. Here, the salt is a subtle contribution.
The cinnamon in the topping is de rigueur, but I also add cardamom because I like the vaguely Scandinavian way it tastes with almonds. Ginger works wonderfully with the grapefruit, so feel free to substitute that if you like it better.
You can also substitute other sweet citrus fruit, trading oranges or tangerines for grapefruit. Really, any tangy fruit will work. Pineapple, raspberries, nectarines and sour cherries all have enough acidity to zip up the heavy molasses flavour and texture of brown sugar. Just skip the salt sprinkle, which isn’t necessary without the bitterness of grapefruit to subdue. And stay away from the likes of blueberries, sweet cherries, peaches and pears, which are too sweet for this supremely sugary dessert.
After all, balancing bitter, sweet, salty and acidic is the key to all good cooking — and, in this case, baking.
Grapefruit Crumb Cake Makes 8 servings
For the crumb topping:
cups all-purpose flour cup light brown sugar 1 teaspoon ground cinnamon
tsp ground cardamom or ginger tsp fine sea salt cup slivered almonds cup unsalted butter (1 stick), melted
For the cake:
2 large red or pink grapefruits
cup plus 1 tablespoon sour cream 3 large eggs
1 tbsp vanilla extract
1 cups all-purpose flour cup granulated sugar tsp baking soda tsp baking powder tsp fine sea salt, more for sprinkling
cup unsalted butter (1 stick), cubed, softened, plus more for greasing the pan
Total time: 1½ hours
1. Heat oven to 350 F and butter a 10-inch springform pan.
2. Make the crumb topping: In a medium bowl, whisk together flour, sugar, cinnamon, cardamom and salt. Stir in almonds and melted butter until ½-inch crumbs form. Store covered in the refrigerator. (You can make the crumb topping up to five days in advance.)
3. Prepare grapefruit: Line a baking sheet or plate with a double layer of paper towels. Finely grate 1 tablespoon of zest from the grapefruit; set aside.
4. Cut top and bottom off grapefruit with a sharp knife, then slice away peel so no white pith remains. Cut out the grapefruit segments by running your knife on the inside edges of each segment, leaving behind the white membranes. Place sections onto the paper-towel-lined pan or plate to dry out slightly. You should have about 1½ cups of grapefruit sections. Pull any large sections apart with your hands so they are all in 1-inch or smaller pieces.
5. Make the cake: In a medium bowl, whisk sour cream, eggs, vanilla and reserved grapefruit zest. In the bowl of an electric mixer fitted with the paddle attachment, mix together the flour, sugar, baking soda, baking powder and salt. Beat in the softened butter for 10 seconds, then beat in the sour cream mixture until smooth.
6. Pour the batter into the prepared springform pan. Spread grapefruit evenly across the top of the cake. Sprinkle the grapefruit very lightly with sea salt, then top with the crumb mixture.
7. Bake until springy when touched, and a toothpick inserted in the centre comes out with just a few crumbs, 50 to 65 minutes. Transfer to a wire rack and cool completely before releasing the sides of the pan and serving (at least two hours).