Ingredients: sourdough discard, lemon zest and extract, all-purpose flour, granulated sugar, butter, eggs, egg yolks, milk, and kosher salt.
Preheat the oven to 325℉. Butter a 9"x5" loaf pan and line with parchment paper.In a small bowl, combine the flour, baking powder, and kosher salt. Set aside.
In a large mixing basin, beat together softened butter and sugar with a hand or stand mixer. Mix for 3-4 minutes, until light and fluffy.
Add eggs and egg yolks to the creamed mixture, one at a time. Beat thoroughly after each addition until the mixture is very frothy and nearly doubled in size.
Combine the sourdough waste, lemon extract, and lemon zest. Beat until thoroughly blended.
Three times, add the dry ingredients to the wet mixture, alternating with two milk portions. Start and finish with dry ingredients. Just blend.
Fill the loaf pan with batter and spread evenly. Bake until a toothpick inserted into the center comes out clean, 60–70 minutes.
Bake for 35–45 minutes, or until a toothpick inserted in the center comes out clean . Transfer the cake to a wire rack to finish cooling after 10 minutes in the pan. Slice and serve