Dry sauté the onion with a pinch of salt until caramelized. Deglaze pan with minimal vermouth. Steam other veggies (except for the basil) separately until just cooked.
In a food processor, mix dry ingredients, then add wet ingredients and blend until smooth. Heat mixture in a saucepan. Whisk until thickened and frothy.
Preheat oven to 450º. In a food processor, combine dry ingredients (except for chickpea flour). Add tofu. With the machine running, very gradually add half the water. Process for 1 minute. Add more as needed until dough forms a ball. Dust a flat surface with chickpea flour and roll out. Flip, dust, and roll repeatedly until quite thin (~1/16 inch). Cut circles to fit your tins. Line with parchment paper for easiest removal.
Fill tins halfway with custard. Add veggies, basil, and sautéed onions on top. Top with a dollop of custard. For 3" quiches, bake 15-20 minutes. For bite-size tartlets, bake 8-12 minutes. Check often and remove when custard turns golden.
Makes 24 mini-tartlets or 12 three-inch individual quiches