Mushroom and sauerkraut pierogi

Mushroom and sauerkraut filling

• 500 g sauerkraut
• 1000 g water
• 1 tbsp grapeseed oil
• 1 onion (approx. 150 g), cut into halves
• 500 g button mushrooms cut into halves
• 1 ½ tsp sea salt to taste
• ¼ tsp ground black pepper to taste

Dough

• 250 g warm water plus extra to seal
• 1 egg
• 2 tbsp grapeseed oil
• 560 g plain flour plus extra to dust
• 1 - 2 pinches sea salt plus extra to boil
• water to boil

Topping

• 120 g salted butter cut into cubes
• 1 large onion diced
• sour cream to serve
• fresh chives finely chopped, to serve