Preheat Josper oven to 300 degrees Celsius. Season the bavette with salt on both sides and a drizzle of grapeseed oil. On the clean grill sear the bavette for 1 minute on each side. Remove and set aside.
To begin making the tartar, whisk the egg yolk, lemon juice and mustard in a bowl. Then slowly whisk in the grapeseed oil to make a quick mayonnaise. Add lemon juice and salt to taste.
Add the beef flank, shallots, avocado, parsley and coriander to the mayonnaise and stir to combine.
Adjust the seasoning with cracked black pepper and salt. Adjust acidity with a squeeze of lemon juice.
Slice the bavette into four even portions and lay onto plates.
Spoon the tartare onto individual plates and garnish with green herbs like sorrel, purslane and pea shoots.
Blend grapeseed oil with the parsley and drizzle over the tartare to finish the dish.
Enjoy with charred sourdough bread.