Step 1
Preheat your oven to 350°F (175°C). Grease a 9×13-inch sheet cake pan or line it with parchment paper for easy removal.

Step 2
In a large mixing bowl, cream the softened butter, granulated sugar, and brown sugar together until light and fluffy—about 3 to 4 minutes using a hand or stand mixer.

Step 3
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Step 4
Mix in the sour cream or Greek yogurt until fully combined. The batter should be thick and smooth.

Step 5
In a separate bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt.

Step 6
Add the dry ingredients to the wet mixture in two batches, alternating with the milk. Start and end with the dry. Mix gently after each addition just until incorporated. Don’t overmix!

Step 7
Pour the batter into the prepared pan and smooth the top with a spatula. Tap the pan on the counter once or twice to release air bubbles.

Step 8
Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden and just slightly springy to the touch.

Step 9
While the cake is baking, start the frosting. In a small saucepan over medium heat, simmer the apple cider until it reduces to about 1/4 cup. This takes 10–15 minutes and concentrates the flavor beautifully.

Step 10
Once the cider has reduced, stir in the butter until melted. Remove from heat and whisk in the powdered sugar, cinnamon, vanilla, and a pinch of salt. Add milk 1 tablespoon at a time if needed to reach a pourable glaze consistency.

Step 11
Let the cake cool for 10–15 minutes, then pour the warm cider frosting over the top, spreading it gently with an offset spatula or the back of a spoon.

Step 12
Let the frosting set slightly before slicing. Serve warm, at room temperature, or chilled—it’s delightful every way.