Ricotta Panna Cotta with Nectarines and Honey

Pour 1/4 cup cold water into a small saucepan and sprinkle gelatin evenly over; let sit 10 minutes to soften.
Meanwhile, coat a 9"-diameter pie or cake pan with a thin film of oil; set aside. Combine ricotta, powdered sugar, vanilla, salt, and 1 cup half-and-half in a food processor.
When gelatin is softened, add remaining 1/2 cup half-and-half to saucepan and set over low heat. Cook, stirring with a heatproof spatula, until gelatin is completely dissolved (do not let mixture boil). Scrape mixture into food processor and process until completely smooth, about 30 seconds. Pour into prepared pan and chill until set, at least 4 hours (cover loosely with plastic wrap after 1 hour).
Run a butter knife or small offset spatula around sides of panna cotta to loosen the edge and break the suction.
Fill a baking dish or similar vessel with hot water. Lower bottom of mold into water 5 seconds, then lift it back out.
Press a serving plate firmly over top. Quickly invert in one motion; set plate down. Use knife or spatula to gently lift up mold.
Top with nectarines; drizzle with honey and oil.
Panna cotta (without nectarines, honey, and oil) can be made 2 days ahead. Keep chilled.