In a large sauté pan, heat 1 tbsp of oil over medium low heat. Add sliced onions and cook for approximately 5 minutes, until onions start to get soft and fragrant.
Begin to add white wine, 1/4 cup at a time. Stir onions occasionally. Wait until first 1/4 cup of wine has dissolved before adding the next.
Cook onions until very soft and deeply golden in color, approximately 35-40 minutes. Place caramelized onions in a bowl and cool completely in the refrigerator. When ready to use, roughly chop caramelized onions.
In a large mixing bowl, combine flour, baking powder and salt. Cut cold butter into cubes and add to the flour mixture. Use a pastry blender to 'cut' the butter into the flour until pea sized pieces of butter remain.
Next, add cold buttermilk and caramelized onions. Mix just until a shaggy dough forms. Turn out dough onto floured surface. Work quickly, and if needed, fold excess flour into dough with a few kneads. Using your hands, form dough into a one inch thick rectangle. Use a biscuit cutter or the top of a drinking glass to cut out 4 biscuits.
Take excess dough and shape into another one inch thick rectangle. Cut biscuits and repeat until all dough is used. Place biscuits on a parchment lined baking sheet. If needed, chill biscuits in the fridge before proceeding.
Preheat oven to 425°F degrees. Brush the tops of each biscuit with melted butter. Sprinkle tops of biscuits with everything bagel seasoning.
Bake biscuits for 20-25 minutes, until fluffy and golden. Allow to cool for 5 minutes before enjoying.