Prepare the apples: In a medium bowl, combine the diced apples with lemon juice and set aside.

Brown the butter: In a medium saucepan, melt the unsalted butter over medium heat. Continue cooking, stirring frequently, until the butter turns a golden brown color and has a nutty aroma, about 5-7 minutes. Be careful not to burn it. Once browned, remove from heat and let it cool slightly.

Mix the wet ingredients: In a large mixing bowl, combine the browned butter and granulated sugar. Whisk until well combined. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Combine the dry ingredients: In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon.

Combine wet and dry mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix. Gently fold in the diced apples.

Prepare the baking pan: Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or line it with parchment paper.

Pour the batter: Pour the batter into the prepared cake pan, smoothing the top with a spatula. Arrange thinly sliced apples on top for decoration, if desired.

Bake the cake: Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden brown.

Cool and serve: Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely. Once cooled, dust with powdered sugar if desired.

Enjoy: Slice the cake and serve it warm or at room temperature. It pairs beautifully with a cup of tea or coffee.