Place 2 Tbsp. of extra virgin olive oil and 2 Tbsp. of butter in a large sauté pan and sauté next 11 ingredients until the vegetables are soft, about 15-20 minutes.
While vegetables are cooking, take salmon and squeeze any excess liquid. This excess liquid is “natural water loss” from the processing.
Allow vegetables to cool to room temperature.
In a large bowl, mix the salmon, breadcrumbs or panko, mayo, mustard, and eggs and toss lightly. Add vegetables when cool.
Shape into desired size croquettes.
Heat the remaining butter and extra virgin olive oil in the large sauté pan over medium heat. Add the croquettes and cook 4-8 minutes on each side until browned.
Drain on paper towels and keep warm in 250 oven until ready to serve!