1. Preheat oven to 350°F.
2. Wash the sole fillets and pat them dry.
3. Cut each fillet of salmon into three equal pieces, against the grain (across the fillet, not lengthwise). You should have six pieces.
4. Place a piece of salmon at the wider end of the fillet of sole.
5. Gently roll the sole around the salmon, securing it with a toothpick once it’s rolled. Repeat with all sole fillets and place them, tightly packed, in a deep baking dish or disposable aluminum pan.
6. Mix ketchup, mayonnaise and dried rosemary and spread evenly over the fish rolls.
7. Bake covered for 15 to 20 minutes and uncovered for another five to 10 minutes. Serve warm or at room temperature.
This recipe is really easy to make in advance. When I make this, I buy the fish fresh and make the rolls, then line them up on a baking pan and place in the freezer. When ready to serve, all you have to do is defrost the rolls fully (do it overnight in the refrigerator) and throw together the sauce. Pour over the fish and bake for one hour. You can then either put it back in the oven to warm before serving or just serve at room temperature.