1Make orange butter:
Stir together all orange butter ingredients in a small bowl until combined well.
Whisk together flour, sugar, baking powder, baking soda, and salt in a bowl. Whisk together buttermilk, 2 tablespoons melted butter, eggs, and vanilla in a large bowl until smooth. Add flour mixture and whisk until just combined. Cut banana into bits and fold into batter along with nuts. (Batter will be very thick.)
3Brush a 12-inch nonstick skillet with some of remaining tablespoon melted butter and heat over moderate heat until hot but not smoking. Working in batches of 3, pour 1/4 cup batter per pancake into hot skillet and cook until bubbles appear on surface and undersides are golden brown, 1 to 2 minutes. Flip pancakes with a spatula and cook until golden brown and cooked through, 1 to 2 minutes more.
4Transfer to a large plate and loosely cover with foil to keep warm, then make more pancakes, brushing skillet with butter for each batch. Serve with orange butter.