Baked Fresh Herring with Potatoes in Tomato-Mustard Marinade

Most people associate herring with cold appetizers and salty brines, but baking fresh fish completely transforms its character. The heat softens the sharp edge of the fish, turning it tender and succulent, while the potatoes tucked underneath act as a sponge, absorbing the savory juices and herbal aromas. The result is a hearty, warming meal where the slight sweetness of the tomato balances the richness of the fish. The Secret to the Flavor The core of this dish is the pre-bake marinade. By combining ketchup and grainy mustard, you create a dual-action coating: the acidity breaks down the fish fibers for a more uniform texture, while the sugars in the tomato base caramelize under the heat, adding depth to the flavor. The layering is equally strategic. Placing the potatoes at the bottom ensures they aren't just a side dish; they slow-cook in the dripping marinade and fish oils, becoming a concentrated part of the overall taste profile.