01 - Preheat your waffle iron according to manufacturer's instructions.
02 - In a large bowl, whisk together flour, poppy seeds, sugar, baking powder, baking soda, and salt until well combined.
03 - In a separate bowl, whisk together milk, eggs, melted butter, lemon zest, lemon juice, and vanilla extract until smooth.
04 - Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix; a few small lumps are acceptable.
05 - Lightly grease the preheated waffle iron. Pour about 1/2 to 3/4 cup batter per waffle, adjusting for iron size. Cook until golden and crisp, approximately 4 to 5 minutes each.
06 - In a small saucepan over medium heat, combine blueberries, water, sugar, and lemon juice. Bring to a simmer, stirring occasionally. Cook until berries burst and syrup thickens, about 6 to 8 minutes. For thicker consistency, stir in cornstarch slurry and simmer 1 to 2 minutes additional.
07 - Serve waffles immediately while warm, generously topped with the homemade blueberry syrup.