Combine the lemon zest, lemon juice, granulated sugar, and strawberries in a saucepan. Bring to a simmer over medium-high heat. Reduce heat to medium and cook the mixture for 12-15 minutes (on the longer side for frozen berries), stirring occasionally, or until the strawberries are very easy to smush with a fork.

Pour the strawberry and lemon mixture into the bowl of a food processor. Add the cornstarch and blend until smooth (you can also add the cornstarch and blend with an immersion blender until smooth). Strain the mixture through a fine mesh sieve over a large bowl, pressing the liquid through as the strawberry solids remain in the sieve.

Chill the mixture for 30-45 minutes, or until at room temperature or cooler. Clean out the food processor bowl and blade (if you used them).

While the strawberry lemon mixture cools, make the crust: preheat the oven to 350 degrees Fahrenheit and prepare an 8 x 8-inch baking pan with parchment paper and spray with non-stick cooking spray.

Add the flour, salt, and granulated sugar to the bowl of a food processor. Pulse a few times to blend.

With the food processor running, drop the cubes of butter one by one into the flour mixture. Run the processor until the dough sticks together and forms a large mass.

Turn the dough out into the baking pan. Gently press down with your fingers or a spatula to evenly spread it into the pan.

Bake the crust for 23-25 minutes, or until the crust just starts to turn golden brown around the edges. Remove the crust from the oven and reduce the oven temperature to 325 degrees Fahrenheit.

Whisk the 4 large eggs into the cooled strawberry lemon mixture until fully combined and a lighter pink color.

Pour the strawberry lemon filling into the still-warm crust. Bake for 40-45 minutes, or until the filling has thickened and just barely jiggles when you nudge the pan with a potholder.

Remove the bars from the oven. Cool on a wire rack at room temperature until it reaches room temperature, or for about an hour. Move to the refrigerator and let chill for up to 2 hours, or until the bars are cool and firm. Slice the bars, sprinkle with powdered sugar (if desired), and enjoy cool!