01 - Combine blueberries, water, sugar, and lemon juice in a medium saucepan. Bring to a simmer over medium heat, stirring occasionally. Cook 8 to 10 minutes, gently mashing some berries. For thicker syrup, stir in cornstarch mixture and cook 1 to 2 minutes until thickened. Remove from heat and set aside.
02 - Preheat your waffle iron according to manufacturer's instructions.
03 - In a large bowl, whisk together flour, poppy seeds, sugar, baking powder, baking soda, and salt.
04 - In a separate bowl, whisk eggs, buttermilk, melted butter, lemon zest, lemon juice, and vanilla extract until well combined.
05 - Pour wet ingredients into dry ingredients and gently stir until just combined. Do not overmix; some lumps are acceptable.
06 - Lightly grease the waffle iron with oil or nonstick spray. Pour batter into preheated iron and cook according to manufacturer's instructions until golden and crisp, about 4 to 5 minutes per batch.
07 - Serve waffles warm with generous ladles of blueberry syrup.