Lightly grease an appropriately sized oven safe baking dish (or use individual ramekins or some kind of small oven safe vessel) with non-stick spray.
In a nonstick pan on medium heat, add the butter, brown sugar, cinnamon, lemon juice, apples, vanilla, and salt. Stir until all ingredients are melted together and combined. Then distribute into the baking vessel(s).
In a bowl, whisk together the flour, walnuts, sugar, baking powder, and milk until a batter forms. Then evenly distribute over the apples.
Bake at 350°F for about 25 - 30 minutes, or until the apples are tender and the top is lightly golden brown. Allow to cool for 5 minutes before serving.
Notes
Pro Tip: Baking vessel should be small enough to contain the ingredients, can also use a muffin tin or ramekins and make individual cobblers.