Any solid object will do, as long as it tolerates the heat. The only reason for using a utensil at all is that your hand does not tolerate the heat (and if it could tolerate the heat, then it would be unsanitary).
When stirring, the important aspect of the spoon is that it’s wide; a flat utensil would work just as well. (However, a spoon has the added benefit of allowing you to taste the soup, as you add salt, herbs, and spices. Use the spoon to pour a little into a small bowl, let it cool there, and then taste it, or you can just blow on the spoon.)
we don’t want to include the water when blending
You can if you want. It’s a trade-off between the trouble of removing the water and the capacity of your blender (or how many batches you want to blend).
In the final product, it’s best to keep as much water as possible, since thrown-out water includes thrown-out vitamins. (The exception is when the water is used to draw out unwanted flavours or other chemicals, which is not the case with ordinary vegetables but can apply to dry beans, for example.) If you have too much water after blending, return everything to the pot and simmer it uncovered until the water level has gone down, stirring occasionally. (Conversely, if your soup is too thick, return it to the pot, add more water, cover, reheat to boiling, and then turn it off.)
If you’re serving the soup right away, it’s nice to return it the pot anyway to keep it warm as people go back for second and third helpings. Use low heat (so that the soup is never too hot to eat), either cover or add water occasionally as needed (let it come back to temperature before serving after adding new water), and stir occasionally to keep it from sticking.
(Boiling water in uncovered pots escapes into the air, but the air inside a covered pot is quickly saturated with water vapour, after which no more water will leave the soup, or at least very little more water if the cover is not air-tight. However, it’s harder to remember to stir when the pot is covered. I often just let the soup thicken a bit through the meal, neither covering the pot nor adding water.)
In the final product, it’s best to keep as much water as possible, since thrown-out water includes thrown-out vitamins.
One way to avoid this trade-off is to microwave the vegetables rather than boiling them. It produces rather similar results otherwise, but doesn’t leach out water-soluble vitamins.
Regarding the blender, and mortar if you are a traditionalist, I would recommend blending without any liquid if possible. The liquid you use should be only enough to carry the food down to the blades in the blender. Any more liquid and you risk the food lifting away from the blades.
A similar problems occurs when mashing, for instance, beans in the mortar and pestle. Liquid allows the larger pieces to glide more easily out of the pestle’s mashing grind.
Any solid object will do, as long as it tolerates the heat. The only reason for using a utensil at all is that your hand does not tolerate the heat (and if it could tolerate the heat, then it would be unsanitary).
When stirring, the important aspect of the spoon is that it’s wide; a flat utensil would work just as well. (However, a spoon has the added benefit of allowing you to taste the soup, as you add salt, herbs, and spices. Use the spoon to pour a little into a small bowl, let it cool there, and then taste it, or you can just blow on the spoon.)
You can if you want. It’s a trade-off between the trouble of removing the water and the capacity of your blender (or how many batches you want to blend).
In the final product, it’s best to keep as much water as possible, since thrown-out water includes thrown-out vitamins. (The exception is when the water is used to draw out unwanted flavours or other chemicals, which is not the case with ordinary vegetables but can apply to dry beans, for example.) If you have too much water after blending, return everything to the pot and simmer it uncovered until the water level has gone down, stirring occasionally. (Conversely, if your soup is too thick, return it to the pot, add more water, cover, reheat to boiling, and then turn it off.)
If you’re serving the soup right away, it’s nice to return it the pot anyway to keep it warm as people go back for second and third helpings. Use low heat (so that the soup is never too hot to eat), either cover or add water occasionally as needed (let it come back to temperature before serving after adding new water), and stir occasionally to keep it from sticking.
(Boiling water in uncovered pots escapes into the air, but the air inside a covered pot is quickly saturated with water vapour, after which no more water will leave the soup, or at least very little more water if the cover is not air-tight. However, it’s harder to remember to stir when the pot is covered. I often just let the soup thicken a bit through the meal, neither covering the pot nor adding water.)
One way to avoid this trade-off is to microwave the vegetables rather than boiling them. It produces rather similar results otherwise, but doesn’t leach out water-soluble vitamins.
Regarding the blender, and mortar if you are a traditionalist, I would recommend blending without any liquid if possible. The liquid you use should be only enough to carry the food down to the blades in the blender. Any more liquid and you risk the food lifting away from the blades.
A similar problems occurs when mashing, for instance, beans in the mortar and pestle. Liquid allows the larger pieces to glide more easily out of the pestle’s mashing grind.