- Butter or cooking spray to coat pan
- 1 cup (200 grams) granulated sugar
- 1/4 teaspoon fine sea or table salt
- Finely grated zest from half a lemon
- 1/2 cup (115 grams) unsalted butter
- 2 large eggs
- 2 teaspoons baking powder
- 1 cup (130 grams) all-purpose flour plus 1/2 cup (65 grams) all-purpose flour, divided
- 1/2 cup (125 grams) sour cream, creme fraiche, or full-fat plain yogurt
- 1 gently heaped cup (140 grams or 5 ounces) fresh raspberries
- 3/4 cup (90 grams) powdered sugar
- 1 tablespoon raspberry puree (for a pink glaze, from a few tablespoons or 1 ounce fresh raspberries), or lemon juice
- 1 to 2 tablespoons milk
Place sugar and salt in a large bowl. Zest lemon into sugar and rub it together with your fingertips; this helps the lemon release the most flavor from it. Add butter and use an electric mixer to beat it with the sugar until fluffy. Add eggs, one at a time, beating well with each addition. Scrape down bowl. Sprinkle cake surface with baking powder and mix it until very well combined. Scrape down sides of bowl again. Add 1 cup (only) of the flour and beat just until it’s no longer visible.
Place raspberries in the bottom of a second medium-large bowl and mash with a fork until mostly broken down but still a little lumpy; you’ll have about 1/2 cup mashed. [If you really dislike raspberry seeds and/or want a smoother look, you can blend the berries until smooth and press them through a fine-mesh strainer — into this second bowl — to remove seeds.] Pour half of the cake batter on top of raspberries (if you have a scale, you can zero out the weight of the bowl and raspberries; half the batter weights 277 grams) but wait, don’t mix it yet.
Instead, go back to the first bowl of batter, the one without raspberries, and add sour cream. Beat to combine. Add 1/4 cup flour, and beat just until smooth. (By beating the “white” batter first, you can reuse you beaters without washing them for the pink batter without muddying the look.)
Beat the raspberries and second half of the cake batter together until smooth. Add final 1/4 cup flour, and beat just until smooth.
Dollop batters in alternating spoonfuls into bottom of prepared loaf pan. Roughly “checkerboard” the rest in, meaning that you’ll drop a pink batter dollop and then a white one and vice-versa until both batters are used up. Drop your pan onto the counter a couple times from a few inches high, to help tap out air bubbles. Use a butter knife or small offset spatula to make a few figure-8s through the batters, marbling them together — but just a little, say, 4 to 5 figure-8s. Any more and the swirls may not look distinct when you cut the cake.
Bake loaf cake for 50 to 55 minutes, or until a toothpick inserted into the center of the cake comes out batter-free. Let cool for 15 minutes in pan, then run a knife around cake and gently remove. Let cake cool completely on rack (I hasten this along in the freezer) before glazing, if using a glaze.
To make your glaze, place powdered sugar in a medium bowl and add raspberry puree (for this, it’s best if you press the berries through a fine-mesh sieve to remove seeds, or it won’t have a smooth pink look) or lemon juice. Whisk to combine, but it will almost definitely be too thick. From here, add milk, a teaspoon at a time, until you can whisk the sugar into a thick but loose glaze. Spoon on top of cooled cake and nudge it to the edges with your spoon or an offset spatual so that it drips where you’d like it to. Cover with sprinkles, if using.
Cake keeps for 4 to 5 days in the fridge. If there’s no milk in your glaze, you can store it at room temperature.