How to Make It
In a large colander set in a bowl, toss the carrots, radishes and cucumbers with 2 tablespoons of the salt. Let stand for 30 minutes.
Meanwhile, in a heatproof medium bowl, cover the porcini with the boiling water and let cool completely, about 30 minutes.
Strain the porcini broth through a fine sieve into a large bowl. Squeeze the mushrooms dry and reserve them for another use. Add the vinegar, garlic, sugar and the remaining 1 1/2 tablespoons of salt to the porcini broth and whisk until the sugar and salt dissolve. Rinse the vegetables and squeeze them dry, then add to the porcini brine. Cover and refrigerate for at least 3 hours or overnight. Drain the pickled vegetables and serve.