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Whole Flounder in the Oven
Instructions
I prepare the ingredients. Two small flounders or one large fish work equivalently.
Fish prep first. The head can stay on or come off — both work. Side fins and tail trim away with kitchen scissors. Belly cleans of the black peritoneal membrane (gives bitter flavour if left). Flounder has no scales, so no scaling needed. Larger specimens may have small spines on the dark side — cut these off.
On the dark (top) side, I make wide diagonal cross cuts — through the backbone, stopping just short of the light (bottom) side. The cuts let marinade penetrate AND create natural portion-divider lines for serving.
For the marinade: vegetable oil, fish seasoning, and lemon juice combine in a deep bowl.
Salt joins.
Then freshly ground pepper and minced garlic.
Finely chopped dill goes in last. I mix until salt fully dissolves.
The marinade coats the fish on both sides; I work the mixture into the cuts. Rest 10 minutes for marinade absorption.
Oven preheats to 180 °C. Meanwhile, onion slices into half-rings.
Baking tray gets foil or parchment lining. Onion half-rings spread out in the centre as a vegetable bed.
The fish places dark-side up on the onion bed.
I cover everything with foil leaving an air space inside (don't let foil touch the fish). The bottom foil edges fold up to form sides, then the top foil seals against those sides. Tray to middle oven rack.
After 30 minutes, I remove the top foil. The fish bakes another 5 minutes uncovered for browning.
Out of the oven. The herbs in the marinade have dried during the bake — scrape them aside when serving (they've done their flavour-infusing job).Each small flounder is 1 serving. The juicy onion bed underneath serves as a built-in side dish. Optional additional sides: mashed potatoes, plain rice, or simple boiled new potatoes. The top dark skin is typically not eaten — peel it back to expose the tender marinade-infused white flesh.Give it a try, enjoy your meal!
Tips
- 1
THE DIAGONAL CROSS CUTS ARE FUNCTIONAL. Step 3's cuts serve dual purposes: they let marinade penetrate the flesh evenly during the brief 10-minute marinate, and they create natural portion-divider lines for serving. Without the cuts, marinade only flavours the surface — the centre stays bland. The cuts should be deep enough to reach the spine but stop before cutting through the bottom skin.
- 2
THE FOIL TENT (NOT WRAP) PREVENTS DRY-OUT. Step 12's "air space inside the foil" technique is calibrated to keep the fish moist while still allowing some browning at the end. Tightly wrapped foil produces steamed-too-soft fish; no foil produces dried-out crispy fish. The tented-with-air-space approach gives the best of both — moist with light crisp. The 30-minute covered + 5-minute uncovered timing is the formula. For another foil-baked flounder variation worth comparing, see Flounder in the Oven in Foil.
- 3
DON'T DEFROST IN HOT WATER. If using frozen flounder, slow-thaw in the fridge overnight (8-10 hours) or 30 minutes in cold-water bath. Hot water defrosting damages the delicate cell structure and produces mushy flesh. The bake itself doesn't fully restore properly-thawed-vs-improperly-thawed differences. Patient thawing is the difference between excellent and mediocre baked flounder.
- 4
WHITE WINE FOR LUXURY VERSION. The base recipe is excellent; for special-occasion dining, replace 1 tbsp of the vegetable oil with 1 tbsp dry white wine (Sauvignon Blanc, Pinot Grigio). The wine evaporates during baking, leaving a subtle sophistication. Add 1 tsp capers to the onion bed for Mediterranean-style. Or top with thin lemon slices in the last 5 minutes for visual elegance. For another whole-fish baked preparation worth trying, try Crucian Carp Baked Whole in the Oven.
FAQ
How do I know when flounder is done? +
Three doneness indicators. First, visual: the flesh turns from translucent to opaque white. Second, fork-test: a fork pressed into the thickest part flakes apart easily without resistance. Third, internal temperature: 60-63 °C at the thickest part is perfect (past 65 °C the fish dries out). The 30-minute covered + 5-minute uncovered timing usually nails 700 g of flounder at 180 °C. For larger fish (1 kg+), add 5-7 minutes to the covered bake time.
What's the difference between flounder, sole, and turbot? +
All are flatfish from the Pleuronectidae family — similar shape, similar mild flavour, similar cooking treatment. Flounder (Pseudopleuronectes americanus, Platichthys flesus) is the most affordable and commonly available. Sole (Solea solea, Microstomus pacificus) is more delicate-fleshed and pricier. Turbot (Scophthalmus maximus) is the largest and most prestigious — typically restaurant-only. This recipe works for any flatfish — adjust cooking time to size (smaller = less time). The technique scales across the family.
Can I add other vegetables to the bed? +
Yes — the onion bed accepts modest additions. Best add-ins: thin-sliced fennel (Mediterranean classic with white fish), thin-sliced lemon (citrus character throughout), cherry tomatoes halved (sweetness contrast), thinly-sliced shallots (for milder onion). Avoid: dense vegetables like carrots or potatoes (don't cook through in the time), watery vegetables like cucumber (dilute the cooking juices). The onion-only bed is the safest choice; veteran cooks add complementary fresh flavours.
What sides go with this? +
Russian-Eastern European tradition pairs whole baked fish with: boiled new potatoes with butter and dill (the classic), simple steamed rice, fresh green salad with vinaigrette, asparagus or green beans (lemon-dressed), or polenta for Italian-style. Avoid: heavy cream sauces (overwhelm the delicate flounder), strong-spiced rice pilafs (compete with fish flavour), or starchy noodles. Mild bright sides are the right counterpart. The onion bed itself often suffices as the only side.
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