Grease a 9-inch baking pan with butter and line it with parchment paper.
Add butter and sugar to the bowl of a stand mixer fitted with a paddle attachment.
Whisk on medium speed until light and fluffy (3-4 minutes). Scrape the sides of the bowl with a silicone spatula a few times while whisking.
Add eggs, one at a time, and mix well after each addition.
Now add flour, baking powder, cinnamon, vanilla extract, yogurt and chopped apples to the bowl and mix just until combined.
Pour the batter into the prepared pan and spread it evenly using a silicon spatula.
Top the batter with apple slices.
Preheat the oven to 350 Degrees F. Keep the pan in the middle rack of the oven and bake for 40-50 minutes or until the top is browned and a toothpick inserted into the center comes out clean.
Remove the pan from the oven and cool the cake for 10 minutes. Transfer the cake to a cooling rack and cool it completely. Cut into slices and serve.