Step 1

Prick sweet potato all over with the tip of a small knife and enclose in plastic wrap.

Step 2

Microwave on high for 10-15 minutes until very tender. Set aside to cool, then halve potatoes and scoop flesh from the skins. Place in a large bowl. Add breadcrumbs, egg, 1 tbs of the sour cream, lemon zest and half the dill, and mix to combine. Season. Fold in salmon, shape fish cake mixture into 12 patties and place in the freezer for 10 minutes.

Step 3

When ready to cook, dust both sides of fish cakes in flour, shaking off excess. Heat 1cm oil in a large fryin pan over medium-high heat and fry fish cakes for 2-3 minutes on each side until golden. Transfer to paper towel to drain.

Step 4

Combine remaining sour cream in a bowl with lemon juice, cornichons and remaining dill. Season. Serve fish cakes with dill sour cream, watercress and lemon wedges.