Line a baking tray with baking paper. Wash the meat, dab dry and place on the baking tray. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
For the crust, whisk mustard, honey and egg. Grate the parmesan. Wash herbs, shake dry, pluck off leaves and chop finely. Peel and wash potatoes, dab dry and grate. Mix potatoes with parmesan, herbs, breadcrumbs and 1 pinch of turmeric.
Stir in mustard mixture. Season with salt and pepper.
Spread the mixture evenly on the meat with your hands (it sticks a bit), press lightly all around and bake in a hot oven for about 25 minutes.
In the meantime peel and finely dice the onion. Wash the tomatoes, possibly halve them depending on size. Heat oil in a pan and fry tomatoes and onion for about 5 minutes. Season to taste with salt and pepper.
Cut the meat open and arrange with the tomatoes. Serve with baguette.