Preheat the oven to 350°F.Add the lemon zest, white and brown sugar, and butter to a stand mixer. Beat on medium-high until well combined and creamy. Add the egg, beating until well combined and resembles frosting, about 3 minutes. Stir in the lemon juice, beer and lemon extract (if using). The mixture may look a little curdled, this is fine. Stir in the flour, baking powder, and salt until just combined.
Line an 8x8 baking pan with parchment so that it comes up and over the sides (this makes for easy removal).
Spread the batter into the prepared pan in an even layer. Bake for 40-45 minutes or until the edges just start to turn golden brown (do not overbake, the bars will set as they cool). Allow to cool before removing from the pan.
Add the cream cheese and strawberries to the bowl of a stand mixer. Beat on high until the strawberries are well combined with the cream cheese and mixture is light and fluffy. Stopping to scrape the sides of the bowl occasionally.
Add the cream, beating well to combine. Add the powdered sugar, stir until combined.
Frost the bars, cut into squares. Chill until ready to serve.
