3 potato patties no Recipes

canned red salmon, cold mashed potatoes (no gravy,pls), unsalted butter, room temp., divided, matzo meal (can use cracker meal), egg, slightly beaten, yellow onion, finely grated (optional), white pepper, salt (i use substitute), fresh lemon zest (fresh is important), light vegetable oil

sweet potatoes (orange peeled chopped into even sized pieces), water (1/3 cup), red salmon (canned no added salt drained bones and skin removed and flaked), corn kernels (casnned drained), breadcrumbs (1/2 cup fresh made from day old wholemeal grain bread), spring onions (green part finely chopped ), egg (50 g lightly whisked ), ground black pepper (or to taste), breadcrumbs (dried 1/2 cup)