Mix the lemon juice, flour and water in a large bowl and soak the celeriac chunks. Do not remove until cooking time to preserve its own color.
Heat a pot or large skillet on medium high. With a slotted spoon, remove the celeriac from the liquid and add to the pot. Add the shallots, potato, carrot, celeriac leaves, orange juice, 1/4 cup olive oil, sugar, 1/3 cup of soaking liquid and salt to taste.
When the water boils, close the lid and reduce the heat to low. Simmer for about 35 minutes. Do not stir it after this stage.
After making sure that all the vegetables are cooked, turn off the heat and then drizzle with 3 Tablespoons olive oil.
Transfer to a serving plate gently and sprinkle chopped dill on top. Serve at room temperature, or after chilling in the refrigerator. Bon appetit!