Place the celery, carrots, onion, tomatoes, zucchini, garlic, mushrooms, basil, rosemary, and parsley into the mixing bowl and chop for 10 seconds/speed 7, using the spatula to assist. Scrape down the sides of the bowl with the spatula.
Add the coarse salt and olive oil. Place the simmering basket on the mixing bowl lid instead of the measuring cup, and cook for 30 minutes/120°C/speed 2.
Remove the simmering basket, place the measuring cup, and blend for 1 minute/speed 4-7, gradually increasing the speed. Transfer the mixture into ice cube trays, let the concentrate cool, then place them in the freezer. The paste concentrate can be stored in the freezer for several months.
1 teaspoon of paste concentrate is equivalent to 1 store-bought stock cube, suitable for 0.5 L.