Layers of strawberry jam add surprise to a lemony loaf.
Preheat oven to 350 degrees. Butter a 9-by-5-by-2 1/2-inch loaf pan. Dust with flour; tap out excess. Sift together flour, baking soda, baking powder, and the salt.
Put egg whites in the bowl of an electric mixer; beat on medium speed until soft peaks form. Add 1/3 cup plus 1 tablespoon sugar; beat until stiff, glossy peaks form. Transfer meringue to a large bowl.
Fit mixer with the paddle. Put butter in a clean mixing bowl; mix on medium-high speed until fluffy, 2 to 3 minutes. Add 1/3 cup plus 1 tablespoon sugar and the zest; mix on medium until pale and fluffy, 3 to 4 minutes. Scrape down sides. Reduce speed to low; add yolks, 1 at a time. Mix in vanilla and lemon juice. Mix in flour mixture in three batches, alternating with two batches of yogurt.
Whisk one-third meringue into batter. Gently fold in remainder with a rubber spatula. Spoon batter into pan.
Bake until firm to the touch and browned and crisp, about 55 minutes. (If top browns too quickly, tent with foil.) Let cool slightly in pan on a wire rack, about 10 minutes. Run a knife around edges to loosen; unmold. Let cool completely.
Cut cake horizontally into three layers. Spread half of jam on bottom layer. Top with middle layer. Spread remaining jam on middle layer. Top with third layer. Refrigerate until set, about 2 hours.
Any other flavor of jam can be swapped in to create different combinations.