Melt the butter in a saucepan. Add the carrots and potatoes and roast them a little. Peel the onion and garlic, cut into small pieces and add to the saucepan. Continue to sweat everything, stirring constantly. Season well with salt and pepper in between. Pour on so much water that everything is a little more than covered. Bring to the boil and simmer covered for 30 minutes at a medium temperature.
Halfway through the process, peel and core the apple and cut into cubes. Peel and finely chop the shallot. Wash the carrot greens, spin dry and roughly chop.
Sweat the bacon in a hot pan. Add bread cubes, apple pieces and shallots. Mix olive oil with honey, add and let everything caramelize a little. Add the crayfish and just reduce the temperature to keep warm. Stir in the chopped carrot greens.
Take the pot off the hob and puree the soup very finely. Season to taste and place in deep plates. Spread the savory, sweet filler on top and decorate with sour cream.