Bring stock to a boil over high heat. Remove from heat add dried mushrooms and set aside to soak for at least 15 minutes or until they are very soft.
Meanwhile, halve the leeks lengthwise, then thinly slice horizontally. Cover with water and let soak for a few minutes to remove any sand or dirt. Carefully lift leeks out of the water and place them on a paper towel-lined plate.
Heat oil in a large frying pan or pot over medium heat. Once oil is shimmering, add leeks, celery, potatoes, carrots, salt and pepper. Cook, stirring occasionally until leeks are tender, about 8 minutes. Add fresh mushrooms, rosemary, and thyme. Cook until the mushrooms have softened, about 5 minutes.
Meanwhile, lift the dried mushrooms out of the soaking liquid. Pour liquid through a coffee filter and reserve. Rinse the dried mushrooms thoroughly to remove any remaining sand. Coarsely chop them, then mix them into vegetable mixture.
Sprinkle flour over the vegetables and cook, stirring, a minute or two until it is slightly toasted and coating all the vegetables. Add the wine and reserved mushroom soaking liquid and frozen peas. Bring to a boil, scraping up any browned bits that have stuck to the bottom of the pot. Taste and add more salt and pepper if necessary. Remove from heat and let cool slightly.
Heat oven to 400°F. Remove thyme and rosemary sprigs and pour into a greased 2.5-3 quart baking dish. Set aside while you make the biscuits
In a medium bowl whisk together flour, sugar, thyme, and rosemary. Set a box grater inside the bowl with the flour mixture and grate the frozen butter through the large holes. Toss the butter shavings with the flour to coat.
Drizzle the milk over the flour and stir to incorporate the milk. The dough should be a wet but not runny. You should be able to loosely shape them into biscuits.
Divide dough into 8 equal-ish sized pieces and pat each piece into a round biscuit shape. You can do this with two spoons or your fingers. Place on top of the filling in the baking dish leaving a little room between each.
Bake for 40-45 minutes or until the biscuits are baked all the way through and the filling is bubbling. Check if the biscuits are baked on the bottom by sticking a toothpick in a spot where two biscuits are touching focusing on the bottom of the biscuits.
Let cool 5-10 minutes then dig in!