Step 1
Preheat oven to 180C fan-forced (200C conventional) and line a large baking tray with baking paper. Toss potatoes in 1 tablespoon of extra virgin olive oil, as well as some salt and pepper, and roast them on the tray for 15-20 minutes until they’re fork-tender and beginning to brown.
Step 2
While the potatoes cook, make the butter. In a small saucepan, saute the garlic and shallot in the 2 tablespoons of olive oil over medium heat for about 4-5 minutes until translucent but not caramelised.
Step 3
Place the butter, herbs, capers, cornichons (or gherkins), lemon zest and juice in a small food processor and blend until mostly smooth. Add the garlic and shallot, along with the olive oil they cooked in, and blend again. Finally, add the egg yolks (if using) and blend once more. You should have a glossy, green emulsified butter. Set aside at room temperature.
Step 4
Coat fish and toss asparagus in the remaining tablespoon of extra virgin olive oil, then season with salt and pepper. (It won’t feel like it’s enough oil, but you only want a thin coating.)
Step 5
Place the fish and asparagus on the baking tray with the potatoes, the asparagus scattered underneath the fish. Bake for about 7-12 minutes, depending on the thickness of the fish. You’ll know the fish is cooked when it wants to flake apart easily in the centre of the fillet. Test this by gently pressing a knife or fork into the top of the fillet and seeing if it wants to break apart. Alternatively, a temperature probe inserted into the middle of the fish should read 52C.
Step 6
Remove the tray from the oven, then spoon the butter over the fish and vegetables, allowing it to melt deliciously over everything. Serve with a simple green salad.
