Preheat the oven to 350℉. Grease the sides and bottom of a 9-inch springform pan* (or 9-inch round cake pan) with cooking spray, then line the bottom with parchment paper. Grease the top of the parchment paper as well.
In a small bowl, whisk together the flour, baking powder, and salt. Set aside.
In a large bowl, add the softened butter and 1 cup granulated sugar. Mix on medium-high speed for 2-3 minutes until pale and fluffy.
Add the egg, yogurt, sourdough discard, and vanilla extract to the butter mixture and mix on low speed until smooth and combined. Slowly add the flour mixture and mix until no dry spots remain.
Transfer the batter to the prepared pan, using a spatula to spread it evenly. Press the halved strawberries into the batter, cut-side down, keeping the berries as close together as possible.
Sprinkle the top of the cake with the remaining 2 Tablespoons of granulated sugar. Bake for 60-65 minutes, until the cake is golden brown and a toothpick inserted in the center comes out clean.
Let the cake cool for at least 30 minutes, then dust with confectioner's sugar and serve.
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Notes
*If you would like to double or triple this recipe, I recommend using two or three 9-inch pans and making each cake in its own pan (rather than using a larger pan). To make this recipe with active sourdough starter, replace the sourdough discard with active starter (200g). You do not need to change any other ingredients in the recipe.