In a saucepan over medium heat, stir together apples, 1/4 cup sugar, and lemon juice; stir constantly until mixture comes to a simmer, then remove from heat.
In a small saucepan over medium heat, melt the butter and cook, swirling the pan occasionally, until it becomes golden in color and takes on a nutty aroma, about 2 to 3 minutes; pour brown butter into an 8 x 8 inch baking dish.
In a mixing bowl, combine flour, 1/2 cup sugar, baking powder and salt; pour in the buttermilk and mix just until dry ingredients are moistened. Spoon the batter on top of the brown butter, using a spatula to smooth out the batter, but being careful to not mix it into the brown butter.
Scatter the apples and juice on top of the batter; sprinkle almonds over top and dust with nutmeg and demerara sugar. Bake until golden, 50 to 55 minutes; transfer pan to wire rack to cool.