These pizzettes are a riff on panissa and farinata, the chickpea-flour specialties from Liguria. The batter is first cooked like crepes and then crisped in a hot oven.
Prepare chickpea flour batter: Place 1 cup water in a small bowl. Sift chickpea flour into it and whisk to blend well. Blend in olive oil, salt, thyme and pepper (if using). Let batter stand at room temperature or refrigerate for at least one hour.
Prepare toppings: In a large skillet, sauté shallot with 2 tablespoons olive oil over medium-high heat until it starts to turn golden. Add mushrooms, cooking until they soften. Add Marsala if using and cook a few minutes longer. Season to taste with salt and pepper.
In a small bowl, combine ricotta with Parmigiano Reggiano and a pinch of salt. Cut tomatoes in halves or quarters. Drizzle with balsamic vinegar and sprinkle lightly with salt.
Cook pizzette crusts: Heat a crepe pan or other small heavy skillet (about 6 inches in diameter)* over medium-high heat, and brush with olive oil. Off heat, pour about 1/3 cup of the batter into the pan and swirl to cover the bottom. Cook, nudging edges with your spatula (this helps with the turning), until the top feels firm and perhaps takes on a leathery appearance, about 2 minutes. Carefully turn and cook about 1 minute. Remove to a plate and repeat with remaining batter, brushing pan with olive oil each time. The pizzettes will be a bit thicker than crepes. (At this point, proceed immediately with recipe or refrigerate crusts and toppings for a few hours.)
If you have a pizza stone, place it in upper third of oven and set temperature to 425°F.
Assemble pizzettes: Spread each crust with ricotta mixture. Top with sautéed mushrooms.
Slide pizzettes onto hot pizza stone or a baking sheet. Cook until ricotta turns bubbly, about 10 minutes (or longer, for extra crispness).
Garnish pizzettes with dressed tomatoes and microgreens. Serve warm or at room temperature.