01 - Preheat your waffle iron according to manufacturer's instructions.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, poppy seeds, and lemon zest.
03 - In another bowl, beat eggs lightly, then add buttermilk, melted butter, vanilla extract, and lemon juice. Mix until combined.
04 - Pour wet ingredients into dry ingredients. Stir gently until just combined; do not overmix as batter may be lumpy.
05 - Lightly grease the waffle iron. Pour an appropriate amount of batter onto the iron and cook according to manufacturer's instructions, until golden and crisp. Repeat with remaining batter.
06 - While waffles cook, prepare the compote: In a small saucepan, combine blueberries, sugar, and lemon juice. Heat over medium heat, stirring occasionally, until berries start to release juices, about 5 minutes.
07 - For a thicker compote, dissolve cornstarch in 2 tablespoons water and stir into the blueberry mixture. Cook 1-2 minutes longer, until thickened.
08 - Serve waffles warm, topped generously with blueberry compote.