This recipe is from Bon Appétit. I made it for breakfast, though it would be a good snacking cake as well. The cake stays moist at room temperature for several days, thanks to the vegetable oil. We all liked it, including the Engineer (who doesn’t normally like grapefruit, but it was subdued enough here that he found it pleasant). The glaze is optional, but recommended.
1½ cups all-purpose flour
2 tsp. baking powder
¾ tsp. kosher salt, plus more
1 Tbsp. finely grated grapefruit zest
1 cup granulated sugar
2 large eggs, room temperature
⅓ cup vegetable oil
1 tsp. vanilla extract
¾ cup plus 1 Tbsp. plain Greek yogurt, divided
8 Tbsp. fresh grapefruit juice, divided
1 Tbsp. poppy seeds, plus more for sprinkling
½ cup powdered sugar, sifted
Preheat oven to 350 °F. Line an 8½x4½" loaf pan, preferably metal, with parchment paper, leaving overhang on the long sides, and lightly coat with nonstick spray.
Whisk flour, baking powder, and ¾ tsp. salt in a medium bowl.
Using your fingers, work grapefruit zest into granulated sugar in a large bowl until sugar starts to clump and mixture is very fragrant, about 1 minute. Add eggs, oil, and vanilla and beat with an electric mixer on high speed until light and thick, about 4 minutes. Reduce speed to low and mix in half of dry ingredients, then mix in ¾ cup yogurt. Mix in remaining dry ingredients followed by 5 Tbsp. grapefruit juice and 1 Tbsp. poppy seeds. Scrape batter into prepared pan and smooth top.
Bake cake until top is golden brown and a tester inserted into the center comes out clean, 50–60 minutes. Transfer pan to a wire rack. Poke holes in top of cake and brush remaining 3 Tbsp. grapefruit juice over top. Let sit 15 minutes, then run a knife around sides to loosen and use parchment paper to lift cake out of pan and onto rack. Remove parchment and let cool completely.
Whisk powdered sugar, remaining 1 Tbsp. yogurt, 1 tsp. water, and a pinch of salt in a medium bowl until smooth and drizzle over cake. Sprinkle with poppy seeds and let sit until glaze is set, about 30 minutes.