Add the flour, sugar and salt to a food processor and pulse just until combined. In a small bowl, whisk mix together the egg, vinegar and water. Add the cold butter pieces into the food processor and pulse until small coarse crumbs remain. Sprinkle the water/egg mixture over the flour and pulse again until the dough comes together.
Remove the dough with your hands and wrap it in plastic wrap. Stick it in the fridge for 30 minutes.
Heat the frozen raspberries and sugar in a saucepan over medium-low heat. Cook until it’s bubbling and the fruit is soft and slightly syrupy, about 10 minutes. Let it cool completely.
Preheat the oven to 375 degrees F. Line a baking sheet with parchment paper. Fill a small bowl with water.
Roll out the dough until it's about 1/4 inch in thickness. Use a 2-inch heart cookie cutter to cut hearts out of the dough. Make sure to cut an even amount since you will press them together!
Place the hearts on the baking sheet. Fill every other round with a teaspoon of the nutella and top with a teaspoon of the raspberry mixture. Dip a finger in the water and run it along the outside of the dough round that has the filling. Place an empty heart on top of the filled heart. Press the outsides down with a fork to seal the hearts together. Repeat with the remaining hearts.
Beat the egg and water together. Brush it on top of all the pies and sprinkle with coarse sugar. Cut and "x" in the top with a paring knife.
Bake the pies for 20 to 25 minutes, or until golden brown. Remove and let cool slightly. Serve with vanilla ice cream!