Preheat oven to 350 degrees Fahrenheit.
Prepare your baking dish by greasing the bottom and sides with a small amount of olive oil.
Peel your potatoes and rinse them under cold running water. Use a mandoline slicer to slice them into thin rounds. If you do not have a mandoline slicer, use a sharp knife to get the thinnest rounds you can, and try to make them all equivalent.
Add 1/2 inch of vegetable oil to a frying pan and heat over medium-high heat. Fry your sliced potato rounds in batches. The potatoes do not need to be thoroughly cooked, but can be slightly browned. Fry for 3 - 4 minutes / side. Remove fried potatoes from hot oil and drain on a paper towel lined dish to remove excess oil. Repeat until all the potato slices are fried.
Rinse your zucchini. Chop off the stem end and then use the mandoline slicer to slice the zucchini into thin rounds.
Place your fried potato slices on the bottom of your baking dish. Be sure to overlap the potatoes. You will likely end up with about 3 layers of potato. Sprinkle with 1/4 teaspoon salt.
Next, layer the zucchini on top of the potatoes. Overlap the zucchini slices and be sure to have at least 2 layers of zucchini. (See Recipe Note)
In a medium sized bowl whisk together the eggs, milk, remaining salt, pepper, baking powder, fresh herbs and the cheeses.
Pour the egg mixture over the zucchini and shake the baking pan around to ensure that the egg is evenly dispersed in the baking pan.
If desired (highly recommended) decorate the top of your frittata with zucchini blossoms. To do so, use a sharp knife to cut off the base of the zucchini blossom and then make a cut lengthwise to open the blossom up. Fan them out decoratively on top of the frittata.
Drizzle the top with olive oil.
Cover the frittata with aluminum foil and bake in the middle rack of your oven for 30 minutes.
Remove cover and bake for an additional 10 minutes.
Allow the frittata to cool and set before serving. Frittata is served best at room temperature or only slightly warm.
Enjoy.