Congee with celery and mushrooms

Name: Congee with celery and mushrooms
Cuisine: Asian
Ingredients: 420g celery; 2 tbsp rice vinegar; 6 tbsp mirin; 20g dried shiitake or porcini mushrooms; 2 tbsp (30g) white miso paste; 2 tbsp olive oil; 250g fresh button or oyster mushrooms, sliced or torn; 1 yellow onion, peeled and finely diced; 2 spring onions, finely sliced, whites and greens separated; 5 garlic cloves, peeled and finely chopped; 1½ tsp sea salt; 2cm x 2cm knob fresh ginger, peeled and grated; 150g jasmine rice; 2 1/2 tbsp soy sauce; Shop-bought or homemade fried onions or shallots, to finish (optional)