1. In a small saucepan, bring water and sugar to a boil to dissolve the sugar for candied lemon slices. Reduce heat and simmer lemon slices for 10 to 15 minutes until translucent. Remove and cool.

2. In a bowl, whisk together flour, baking powder, baking soda (if using), sugar, and salt. In a separate bowl, combine ricotta, milk, egg yolks, vanilla, lemon zest and juice, and poppy seeds.

3. Gently fold the dry ingredients into the wet until just incorporated, leaving small lumps. Beat egg whites until stiff peaks form, then carefully fold into the batter.

4. Heat a buttered griddle or skillet over medium-high heat. Pour about 1/3 cup of batter per pancake. Cook until bubbles form and edges look set, about 3-4 minutes. Flip and cook another 3-4 minutes until golden brown. Adjust heat as necessary.

5. For optional blueberry sauce, mix lemon juice and cornstarch in a bowl. In a saucepan over high heat, combine blueberries, sugar, water, and salt; bring to a boil for 1 minute. Simmer, stir in lemon juice mixture, and cook until thickened, about 5 minutes. Serve warm over pancakes.