In a blender, pulse 2 handfuls of spinach leaves with 1 1/4 cups water.
Strain spinach liquid through a mine-mesh strainer and reserve liquid.
In a large bowl, combine flour with 3/4 cup spinach liquid using a chopstick.
When dough comes together, transfer to a floured work surface and knead for 10-15 minutes until smooth.
Wrap dough in cling film and rest in the fridge for at least 30 minutes. It can last up to a day.
In a large bowl, combine ground pork with salt, pepper, maple syrup, basil, garlic, ginger, vinegar, and diced apples.
When ready to roll the dumplings, remove dough from fridge. Cut into 4 equal pieces.
On a floured work surface, roll each piece into a log (about 8" long).
Cut each log into 6 pieces. Roll the pieces in flour.
One at a time, press down on your piece and roll with a rolling pin into a round wrapper, about the size of a drink coaster.
Fill each wrapper with about a tablespoon of filling. Press the dough together in the middle and crimp the edges on both sides. Follow a diagram online for best results.
When the dumplings are ready, heat 1 tbsp oil in a non-stick pan over medium-high heat. If cooking all at once, use two pans (each pan should have a lid).
When oil is heated, place dumplings flat side down in oil and cook for 2 minutes until crisp.
Carefully add 1/3 cup water to each pan and immediately cover with a lid. Turn heat down slightly and cook for 6 minutes.
Serve with soy sauce or your favorite dipping sauce.