Slice the kangaroo fillet into thin slices, three per serving. Brush with olive oil and sprinkle lightly with black pepper; set aside.
Remove stalks from spinach and wash leaves thoroughly. Plunge into rapidly boiling water for 30 seconds. Strain and immerse immediately in iced water to stop the cooking process and maintain the colour. When cold, remove leaves from water and squeeze out as much liquid as possible. Refrigerate until ready to use.
Soften 100g of unsalted butter and blend in food processor with the anchovies, lemon juice and a pinch of sea salt until smooth. Scrape out onto a piece of foil and form into a sausage shape. Refrigerate until firm.
Heat a large, heavy- base, cast-iron fry pan to hot. Add the oiled kangaroo meat slices and quickly sear on each side. Do not turn until the first side is properly, it will lift easily. Stay with it, be sure not to over-cook. Remove meat and rest in a warm place until all the meat slices are cooked.
In another pan, over medium heat, melt the remaining butter, add the squeezed spinach and the salt. Stir until the spinach is hot. Divide the spinach into four portions, spoon onto the centre of the plate, top with three escalopes of kangaroo.
Place the anchovy butter so it begins to melt over the hot meat. Serve immediately.