Step 1

Preheat oven to 350°F. Line a 15x10-inch baking pan with foil, extending foil over edges. Remove 4 tsp. zest and squeeze 5 Tbsp. juice from limes.

Step 2

In a large bowl beat butter and shortening with a mixer on medium to high 30 seconds. Add 3 tsp. of the lime zest, the granulated sugar, baking powder, and salt. Beat until light and fluffy, scraping bowl as needed. Beat in eggs, vanilla, and 3 Tbsp. of the lime juice until combined. Beat in flour. Spread batter into prepared baking pan.

Step 3

Bake 20 to 25 minutes or until light brown. Cool slightly in pan on a wire rack.

Step 4

For glaze, in a small bowl stir together powdered sugar, remaining 1 tsp. lime zest, and 4 tsp. of the lime juice. If needed, stir in enough of the remaining lime juice to reach a thin glazing consistency. Spread warm uncut bars with glaze; cool. Using foil, lift out uncut bars. Cut into bars.