For the blueberries: Macerate the blueberries by mixing them together with the sugar and balsamic vinegar in a small bowl. Set aside while you make the ricotta mix and the bruschetta.
For the lemon ricotta: Add the ricotta, heavy cream, lemon zest and juice, salt and pepper to the bowl of a food processor. Mix until the ricotta is smooth and fluffy, 1 to 2 minutes.
For the crostini: Heat a griddle (or large cast-iron skillet) over medium-high heat. Spread each side of the sliced bread with some butter. Toast the bread on both sides until crisp and golden, 1 to 2 minutes per side. Allow the bread to cool slightly.
For serving: To assemble, smear a heaping tablespoon of the lemon-ricotta mixture onto a piece of toasted bread. Top with a tablespoon of the macerated blueberries and garnish with a basil leaf. Transfer the bruschetta to a platter and drizzle with the balsamic glaze. Zest the lemon over the platter before serving.