Preheat oven to 350°F.
In bowl, mix together flour, sugar and salt.
Split vanilla pod, scrape out seeds and mix with milk, lemon zest and lemon juice in separate bowl. Sift in dry ingredients and whisk together until smooth. Add ricotta and whisk until smooth. Whisk in eggs one at a time until smooth.
Put butter in large cast-iron pan and place in preheated oven until butter has melted and pan is hot. Pour batter into hot pan and top with blueberries. Return pan to oven and bake until pancake has set completely, 30 to 35 minutes.
To serve, top with more blueberries, powdered sugar and maple syrup, if desired.