Preheat oven to 350°F and prepare a 9x9-inch pan by lining it with parchment paper (or lightly grease and flour). (You could use a 9x13-inch pan for more servings, but the bars will be thinner.)
In a large bowl, combine the melted butter and brown sugar. Stir well.
Add the eggs and the egg yolk, one at a time, stirring well after each addition.
Stir in the lemon juice and lemon zest.
In a separate, medium-sized bowl, whisk together the flour, cornstarch, baking powder, and salt.
Gradually stir the flour mixture into the butter and egg mixture until completely combined.
Fold in strawberries.
Spread the batter evenly into the prepared pan. Bake 45-50 minutes, or until the edges are turning golden brown. (If you are using a 9x13-inch pan, bake for 25-30 minutes.)
Remove from oven and allow blondies to cool before glazing.