Soak the brains in salted cold water for 2 hours, changing the water every 30 minutes. Drain, carefully remove the membrane using a sharp knife. Rinse brains well.
Roughly chop 1 rasher bacon and finely dice the other. Place brains in a saucepan of cold water with a good pinch salt and the roughly chopped bacon and bring to boiling point over low heat. Drain then transfer to a tray and refrigerate until cold
Pour milk into a saucepan, add parmesan rind and pinch salt and bring to simmer over medium heat. Cook the potato in a saucepan of salted water until tender. Drain. Strain the milk discarding the parmesan rind. Combine milk in blender with potato, blend until smooth.
Preheat oven 180C fan forced. Line a baking tray with baking paper. Sprinkle grated parmesan over the baking paper in 10-15cm rounds. Bake 8-10 minutes or until light golden. Set aside to cool.
Heat olive oil in a frying pan over medium-high heat. Add mushrooms, garlic and diced bacon and cook 5 minutes, turning mushrooms until light golden and tender. Drain on paper towel.
Toss the apple batons with olive oil and a pinch salt. Half-fill a saucepan with oil and heat over medium heat until hot.
Pat brains dry with paper towel then coat in flour, egg and breadcrumbs. Deep fry brains 30 seconds until golden. Drain on paper towel and season with salt.
Combine milk and potato mixture in a cream gun (foam canister) and gas with two soda bulbs (see note below).
To serve, arrange mushrooms on the serving plate. Top with brains and dressed apple. Top with milk froth, parmesan crisp and sprinkle with bacon crumble.
Notes: Cream gun or foam canister along with soda bulbs are available from chef supply outlets