Melt butter and extra virgin olive oil in a large Dutch oven or soup pot over medium heat. Add leeks and shallot, season with salt and pepper, then saute until leeks are tender and beginning to turn golden brown, 15 minutes. Add garlic then saute until very fragrant, 2-3 minutes.
Add canned tomatoes, seafood stock, chicken stock, dried thyme, and bay leaf then turn heat up to bring to a simmer. Turn heat back down to medium-low then simmer for 10 minutes. Add potatoes then place a lid partially on top and simmer until potatoes are tender, 20-30 minutes, stirring occasionally. Taste then add salt and pepper if necessary.
Turn heat to medium-high then add the seafood and parsley and cook for 2-3 minutes or until the seafood is barely cooked through — the seafood will continue to cook from the heat of the soup/pot, so don’t overcook!
Remove pot from heat then add a drizzle of fresh lemon juice (start with a little as you can always add more.) Scoop into bowls then serve immediately.
Notes
If you prefer petite diced versus regular diced tomatoes, use a pair of kitchen shears to snip the tomatoes in the can after opening.
I like a combination of scallops sliced in half widthwise, halibut cut into 1” cubes, and peeled/deveined jumbo shrimp.
For crostini: Slice a gluten-free baguette (or regular baguette if you don’t need to eat GF) into 1/4" slices then brush both sides with extra virgin olive oil and season lightly with salt and pepper. Arrange on a sheet pan then bake at 350 degrees for 5-7 minutes, or until golden brown, flipping slices halfway through. Let cool completely.