Melt the 50 g butter in a large heavy-based pan and sauté the shallots until glassy. Add the thyme and rice and fry while stirring until the rice looks glassy with a white core. Add the wine and keep on stirring. Fold in the hot stock, spoonful by spoonful, on high heat and continue to stir until absorbed. After 15 minutes, add the beetroot cubes. Continue until the rice is cooked al dente in 20 minutes. Season with salt and pepper. Stir in the cheese until fully melted and the remaining cubed butter. Turn off the heat and place the lid on the pan. Quickly transfer the risotto to four plates and serve.