Line a baking sheet with parchment paper. Spoon 8 mounds of nutella onto it, about 1 1/2 tablespoons each, flatten into 2 inch discs, and freeze for at least 30 minutes until solid.
Stir the vinegar into the milk and let it sit 5 minutes to create quick buttermilk.
Whisk the flour, sugar, baking powder, baking soda, and salt in a large bowl.
Whisk the melted butter and vanilla into the milk mixture, then pour into the dry ingredients and stir just until combined. Rest the batter 5 minutes.
Heat a greased griddle over medium heat. Pour 1/4 cup batter per pancake, immediately place a frozen nutella disc in the center of each, and cover with 2 more tablespoons of batter to seal it inside.
Cook until bubbles appear and the edges look set, about 3 minutes, then flip and cook 2 to 3 minutes more until golden.
Dust with powdered sugar and serve warm so every pancake pulls apart with a molten chocolate hazelnut center.
