01 - Preheat your waffle iron according to manufacturer's instructions until ready for use.
02 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, poppy seeds, and lemon zest until well blended.
03 - In a separate bowl, beat eggs lightly, then add buttermilk, melted butter, vanilla extract, and lemon juice. Whisk until fully combined.
04 - Pour wet ingredients into dry ingredients. Stir gently with a spatula until just combined; do not overmix. The batter should remain slightly lumpy.
05 - Lightly grease the preheated waffle iron. Pour appropriate amount of batter onto the iron and cook according to manufacturer's instructions until golden brown and crisp. Repeat with remaining batter.
06 - While waffles cook, combine blueberries, sugar, and lemon juice in a small saucepan over medium heat. Stir occasionally until berries begin to release juices, about 5 minutes.
07 - For thicker consistency, dissolve cornstarch in water and stir into blueberry mixture. Continue cooking 1-2 minutes until compote thickens nicely.
08 - Serve warm waffles immediately, topped generously with warm blueberry compote.