- Preheat oven to 350°F. Lightly spray an 8x8-inch baking dish with nonstick cooking spray. 
- In a medium bowl, mix together the softened butter, flour, and granulated sugar until the mixture is crumbly but holds together when pressed. 
- Press the crust mixture firmly and evenly into the bottom of the prepared pan using your fingers or the bottom of a measuring cup. 
- Bake for 15 to 20 minutes, or until the edges are lightly golden. 
- While the crust is baking, in a medium bowl, whisk together the lightly beaten eggs, granulated sugar, flour, baking powder, lime juice, and lime zest until smooth. 
- Pour the lime filling over the hot crust as soon as the crust comes out of the oven. 
- Return the pan to the oven and bake for an additional 15-20 minutes, or until the filling is just set in the center and the edges are lightly golden. 
- Remove from oven and dust immediately with confectioners’ sugar. 
- Allow the bars to cool completely at room temperature, then refrigerate overnight for best texture. 
- Cut into squares and serve chilled.