Saute carrot,celery,leek in a nonstick pan using 1 tbsp olive oil, until tender. Puree vegetables with 1/2 cup of fish stock until a thick paste in texture, (will have fine chunks)set aside.
Use other tbsp of olive oil to saute lobster tails in shells over medium heat until almost done, season with salt and pepper. Add minced garlic to pan with tails and remove from heat. Deglaze pan with 1/2 cup of fish stock and allow to cool.
I use the pan that I sauteed the vegetables in to build my bisque. Add remaining 3 cups of fish stock to pan, heat on medium heat until bubbling. Add puree and tomato paste and whisk. Remove lobster meat from tails and cut into large pieces. Pour fish stock from lobster pan back into bisque and add lobster meat. Reduce heat to low, add milk and sour cream and whisk to combine.
Remove from heat, garnish with parsley and serve immediately.