Preheat the Oven – Preheat your oven to 350°F (175°C). Grease a rectangular sheet pan or line it with parchment paper.
Prepare the Dry Ingredients – In a bowl, sift together flour, baking powder, baking soda, and salt to ensure even distribution.
Mix Butter and Sugar – In a large mixing bowl, beat softened butter and sugar until light and fluffy.
Add Eggs – Add eggs one at a time, mixing well after each addition to create a smooth batter.
Incorporate Kefir – Slowly pour in the kefir while mixing. This helps create a tender texture.
Combine Dry and Wet Ingredients – Gradually add the dry ingredients to the wet mixture. Gently fold the batter until just combined. Avoid overmixing.
Add Vanilla Extract – Stir in the vanilla extract for added flavor. Optionally, fold in chocolate chips, citrus zest, or nuts.
Pour the Batter – Evenly pour the batter into the prepared baking pan and smooth the top with a spatula.
Bake the Cake – Place the pan in the preheated oven and bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean.
Cool the Cake – Let the cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.
Decorate and Serve – Dust with powdered sugar, drizzle with a simple glaze, or spread frosting as desired. Enjoy your homemade kefir sheet cake!