Preheat oven to 350°F (175°C). Grease a 9×13 pan and line the bottom with parchment for easy removal. In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt until evenly mixed—this keeps your spice swirl consistent.

In a separate bowl, beat granulated sugar, brown sugar, eggs, yogurt, oil, and vanilla until smooth and slightly pale (about 2 minutes). A handheld mixer or stand mixer works fine here—no need for heavy equipment.

Gently fold the dry mixture into the wet—stop when just combined. Overmixing can make your cake dense, so be gentle. Stir in the lemon zest, then fold in diced apples and nuts (if using), so every bite bursts with fruit.

Spread batter evenly in the pan, smoothing the top with a spatula. Sprinkle a light dusting of cinnamon sugar on top for a sparkling finish. Bake 35–40 minutes, or until a toothpick in the center comes out with just a few crumbs. Your kitchen will smell heavenly—almost therapeutic!

Let the cake cool in the pan for 15 minutes, then lift out using the parchment and transfer to a wire rack. Cool another 10 minutes before slicing into 12–14 squares—warm slices taste divine, but they hold together best when slightly cooled.