Preheat the oven to 400°F. Line a half sheet pan with parchment paper or a silicone baking mat .
Remove the grapes from the stems, rinse clean, and pat dry. In a large bowl, whisk the Herbes de Provence and balsamic vinegar into the grape seed oil to emulsify to a dressing. Gently toss the grapes into the dressing, to coat. Scatter the grapes onto the prepared baking sheet, scraping any residual dressing over top. Roast the grapes for 12 to 15 minutes, or until the skins begin to pop open. Remove the roasted grapes from the oven.
While the grapes are roasting, lightly brush both sides of the slices of bread with melted butter. Toast the buttered slices on a hot griddle until browned on both sides. Arrange the toasts on to a serving platter.
Fold the grated Fontina cheese into the ricotta to combine. Smear each toast with the ricotta mixture. Divide the roasted grapes evenly between the crostini. Sprinkle kosher salt and freshly cracked pepper over all, to taste. Garnish with freshly chopped parsley, if desired.