Step 1

PreparationSyrup: Bring lemon zest, sugar, and ⅔ cup water to a boil in a heavy medium saucepan, stirring until sugar dissolves. Cook (do not stir) until a thin syrup forms, 6–8 minutes. Add blueberries and bring to a simmer. Reduce heat to medium; cook, stirring constantly, 2 minutes.

Step 2

Transfer 2 Tbsp. syrup to a small bowl, add cornstarch, and stir until smooth. Add back to syrup; simmer until thickened, about 1 minute. Remove from heat. Fish out lemon zest and discard. Squeeze in lemon juice to taste and let cool slightly.

Step 3

Waffles and assembly: Whisk flour, oats, baking powder, baking soda, and salt in a large bowl. Make a well in the center and add yogurt, then melted butter, then egg to well. Using a fork, stir together wet ingredients, then mix, incorporating dry ingredients a little at a time, until a lumpy batter forms.

Step 4

Heat waffle iron on medium-low. Lightly coat with nonstick spray and pour a heaping ½ cup batter onto iron (or up to 2 cups if using a larger one). Cook until waffles are golden brown and cooked through, about 5 minutes. (Keep warm on a baking sheet in a 300° oven if desired.) Repeat with remaining batter, coating iron with more nonstick spray as needed. Serve with butter and warm syrup.