Heat a couple of tablespoons EVOO, 2 turns of the pan, over medium-high heat in a large soup pot or dutch oven. Add the butter to melt, then add carrots, celery and onions; season with salt, pepper and bay leaf. Cover pot and cook, stirring occasionally, until the carrots soften, 7 to 8 minutes. Sprinkle the flour on the vegetables and stir for a minute, then whisk in the chicken (or vegetable) stock until thickened. Stir in the mustard and peas. For a thinner soup, add 1 to 1 cups water with the stock.
Add the chopped fresh herbs to the biscuit batter and combine. When the soup is bubbling, form the batter into small dumplings using two spoons, then drop onto the surface of the soup. Cover the pot with a tight-fitting lid and cook the dumplings, gently stirring, until just firm, 8 to 10 minutes. Transfer the soup and dumplings to shallow bowls; discard the bay leaf.