Preheat oven to 350°F. Spray a 9x13 pan with non-stick spray.
In the bowl of a stand mixer (you can use an electric hand mixer too), combine butter and sugar and beat on medium speed until light and fluffy. Add egg, lemon juice, Princess emulsion, and lemon zest. Mix on medium until well combined, scraping down the sides as needed.
Add flour, baking soda, salt, and poppy seeds and mix. Mix on low until incorporated and then increase speed to medium and mix until well combined, scraping down the sides as needed.
Press evenly into prepared baking dish. Bake for 20 minutes or until golden brown. Place on a wire rack and cool completely.
When the bars are cool, prepare the glaze by whisking together the powdered sugar and water. Spread evenly over bars. Let harden before cutting into squares.
Store in an airtight container.
If Meyer lemons are unavailable, regular lemons will work fine.