Preheat the oven to 415 degrees. Prepare a baking sheet with a sheet of parchment paper.
Combine the flour, brown sugar, baking powder, salt, and cinnamon in a large bowl. Stir in the oats. Use a pastry cutter or the back of a fork to cut the butter into the dry ingredients until it is reduced to pea-sized clumps.
In a separate bowl, combine the milk and maple syrup. Pour the mixture into the dry ingredients and butter and fold just until combined.
Turn the mixture out onto a floured surface. Gently pat together, but be careful not to overwork. Pat out to 1” thickness and then fold in thirds like a letter. Rotate the dough 90 degrees and then repeat this patting and folding process. Repeat once more for a total of 3 sets of folds. Pat the dough out to 1” thickness and use a floured biscuit cutter to cut out rounds of dough. Gently pat together the remnants and cut out more biscuits.
Combine the melted butter and remaining maple syrup together and brush over the tops of the biscuits. Bake in the preheated oven for about 12-15 minutes, or until the tops are golden brown.