Fry the shallots with fennel, thyme, bay leaf and cardamom. Deglaze with white wine and add the shellfish fond. Reduce until desired consistency. Pass through a sieve. Finish with butter and vanilla. Season.
Braize the onion in olive oil. Add the pineapple and cook briefly. Add sugar and let caramelize. Add the citrus vinegar and mango. Simmer shortly. Season to taste and add some freshly grated zest of lime.
Season the foie gras slices with salt and pepper; then fry.