To make the onion tartlet, half the onion, be sure to keep the outer layer of the onion skin on! In a small heavy-based oven-proof pan, place it face-side down in the pan on a low heat and gently caramelise until golden brown. Whilst it is caramelising, put the oven at 160C to preheat. Once caramelised, cover the onion in the pan in tinfoil and place into oven at 160C for around 40 minutes. After 40 minutes, remove the pan from oven. Take the skin off the onion whilst you prepare the pastry. Increase the temperature of the oven to 220C.
With your rolled out rough puff pastry, cut a side plate sized circle that will cover the onion. Place the pastry over the top of the onion in the pan and then egg wash the top. Pop the onion tart into the oven at 220C for around 15-20 mins or until golden brown. Remove from the oven and turn the pan upside down to remove the onion tar. Into the still hot pan, carefully put in the sugar with a good splash of water. Place on the stove, bring to a boil and reduce the caramelised sugar mixture by half. Once this is made, you can use this syrup to glaze the onion tart.
To make the venison rack, heat a heavy-based oven-proof frying pan on a medium-high heat and pre-heat the oven to 180C. To prepare the rack, season it with salt and pepper and a splash of oil. Once the pan has been heated, carefully place the rack into the pan to sear and caramelise the sides. This should take about 10 minutes. Once all sides have been beautifully bronzed, add the butter, sage and thyme to the pan. Baste the rack with this buttery herby mix for around 5 minutes. Place the pan with the rack into the oven at 180C for around 20 minutes or until a core temperature of 40C has been reached. Ensure that the rack is rested for around 10 minutes before slicing and serving.
With the sprout tops, when the rack is resting, sautee the sprout tops with a knob of butter and splash of olive oil under wilted but still al dente.
To serve, slice the rack with the tartlet and sprouts with a good glug of savoury gravy. A delightful dish that will blow any guest away.