Place the dried cremini mushroom in a bowl, add 2 cups of hot water and let it soak to soften for about 20-30 minutes. Rinse the soaked mushroom from its soaking liquid as you transfer it to another bowl, make sure to wash off any hidden, stubborn grits. Let the grits subside at the bottom and slowly pour the liquid into another bowl leaving the grits behind. Or, strain the liquid using a coffee filter or a cheesecloth.
Add the butter to the pan and melt over medium-low heat. Once heated, add the onion and celery and let it sweat until the vegetables are soft about 3 minutes. Add the mushroom and ½ teaspoon of salt and cook until the mushrooms release their juices and evaporate. The mushroom should be caramelized a little.
Add the porcini mushroom and garlic, cook for a minute. Add the rolled oats, chicken stock, bay leaf, thyme and the strained porcini liquid.
Increase the heat to boil. Once you reach the boiling point, lower the heat to medium-low and let it simmer steadily with the lid on but slightly ajar until the rolled oats lose their shape lending a thicker consistency, and the mushrooms are tender for about 20-25 minutes. Fish out the bay leaf and discard, add the remaining salt and pepper, stir, taste and add more seasoning if necessary. Drizzle the lemon juice and serve garnished with parsley leaves.
