For the Bars:

In an electric mixer or a standing mixer fitted with the whisk attachment, cream the butter and powdered sugar on medium speed until fluffy, around 3 minutes. Add the flour, wheat germ, and salt, and beat until combined. Press the dough into a 9 × 13-inch baking pan, distributing it evenly and making sure you cover the sides of the pan as well as the bottom. Let chill in the refrigerator while you preheat the oven to 350°F.

Bake for 15 to 20 minutes, or until the crust is light brown and set. Let cool completely.

Meanwhile, whisk all the filling ingredients together in a medium bowl.

Pour the filling into the cooled crust and bake for 25 to 30 minutes, or until the filling is set.

Sprinkle the bars with sifted powdered sugar, and decorate them with Candied Lemon or Lime Slices if desired.

Chill until cold and slice the bars using a knife dipped in hot water.

Place the cut bars on a stacked serving tray or on a plate.

For the Candied Lemon Slices:

Slice the lemons as thin as possible, about 1/8 inch thick, and remove any seeds.

Cut sheets of wax paper and place them underneath a wire cooling rack.

Combine the sugar and 1 cup water in a small heavy-bottomed saucepan, and cook over high heat until the sugar dissolves and the mixture is boiling. Add the lemon slices and let the mixture simmer over medium-low heat for 15 minutes, or until the lemon slices are opaque. Make sure the sugar mixture does not begin to caramelize.

Using a fork or a slotted spoon, carefully transfer the lemon slices to the wire cooling rack, arranging them in a single layer. Let them dry for at least 1 hour. The lemon slices should be slightly sticky.

Extra slices, placed between pieces of wax or parchment paper and placed in an airtight container, can be frozen for up to 2 weeks or refrigerated for 1 week.