Ingredients

• Nonstick vegetable oil spray
• 1 1/2 cups all-purpose flour
• 2 teaspoons baking powder
• 3/4 teaspoon kosher salt, plus more
• 1 tablespoon finely grated grapefruit zest
• 1 cup granulated sugar
• 2 large eggs, room temperature
• 1/3 cup vegetable oil
• 1 teaspoon vanilla extract
• 3/4 cup plus 1 tablespoon plain Greek yogurt
• 8 tablespoons fresh grapefruit juice, divided
• 1 tablespoon poppy seeds, plus more for sprinkling
• 1/2 cup powdered sugar

Instructions

1. Preheat oven to 350°F. Line an 8 1/2-by-4 1/2–inch loaf pan, preferably metal, with parchment paper, leaving overhang on the long sides, and lightly coat with nonstick spray. Whisk flour, baking powder, and 3/4 tsp. salt in a medium bowl.
2. 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 3/4 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.
3. Bake cake until top is golden brown and a tester inserted into the center comes out clean, 50 to 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.
4. 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.
5. Do Ahead Loaf can be baked and glazed 3 days ahead. Store airtight at room temperature.
6. Loaf can be baked and glazed 3 days ahead. Store airtight at room temperature.