Preheat your oven to 350°F (175°C) and grease a 9-inch round or square cake pan.
In a medium bowl, toss the cubed apples with the sugar and cinnamon. Let sit for 10 minutes to release their natural juices.
Prepare your cake batter and gently fold in the apple mixture, or pour half the batter into the pan, layer with apples, then top with the remaining batter for a layered effect.
Bake for 35–45 minutes, or until a toothpick inserted in the center comes out clean and the top is golden brown.
Let cool slightly before slicing. Serve warm or at room temperature.