Preheat the oven to 350 degrees
Melt 2 tablespoons of butter in a large skillet over medium heat and add the peeled and sliced apples with 1 tablespoon of brown sugar. Mix to combine and stir occasionally until the apples begin to soften and then set them aside
Place a 10" shallow baking dish with 2 tablespoons of butter into the preheating oven until the dish is hot and the butter is melted
While the oven is preheating, add 3 eggs, 1 cup of whole milk, 1/2 cup of granulated sugar, 1/2 teaspoon of salt, 1 tablespoon of vanilla extract, 2 teaspoons of lemon zest and 1/2 cup of all purpose flour into a large bowl and whisk vigorously until frothy and completely combined
Remove the preheated dish from the oven and set it onto a flat, heat proof surface
Carefully pour the batter into the dish
Add the softened apples evenly throughout the batter, sprinkle a tablespoon of coarse grained sugar over the top and return it to the oven immediately
Bake at 350 degrees on a middle rack for about 26-28 minutes
Once the clafoutis is puffed and the edges are browned, remove it from the oven
Allow it to cool for 5 minutes and dust with confectioners sugar before enjoying.