1. Preheat the oven to 350°F (175°C) and line a 9×9-inch square baking pan with parchment paper for easy removal.
2. Cream the butter and sugar together until light and fluffy, about 30 seconds to 1 minute.
3. Beat in the egg (and egg yolk, if using), then mix in lemon juice and lemon zest until combined.
4. In a separate bowl, whisk together flour, baking powder (or baking soda), and salt. Gradually add dry ingredients to the wet mixture, stirring just until no dry flour remains. Avoid overmixing to keep blondies tender.
5. Gently fold in the diced fresh strawberries, tossing them lightly in flour beforehand can help prevent sinking.
6. Spread the batter evenly into the prepared pan using a spatula. Optionally, press a few strawberry slices on top for presentation.
7. Bake for 30 to 45 minutes—depending on pan size and oven—until the edges are golden and a toothpick inserted near the center comes out with moist crumbs. For a 9×9 inch pan, closer to 45 minutes; for a 9×13 inch pan, reduce baking time accordingly.
8. Allow the blondies to cool completely on a wire rack before glazing to prevent the glaze from melting.
9. For the glaze, puree fresh strawberries and strain to get about 1 tablespoon of puree (or use strawberry jam), then whisk together with powdered sugar and lemon juice until smooth. Adjust glaze thickness by adding more powdered sugar or lemon juice as needed. Spread the glaze evenly over the cooled blondies and let set before slicing.