Trim the crust off all sides of the pound cake with a long serrated knife, so you are left with a clean rectangle.

Slice the cake horizontally into 2 even layers.

Brush the warmed apricot jam over the bottom layer, then replace the top layer and press gently.

Chill the cake for 30 minutes so it firms up and cuts cleanly.

Trim the sides square, then cut the cake into 24 small cubes or rectangles, about 1.5 inches each.

Place the cubes on a wire rack set over a baking sheet, spaced apart so icing can drip freely.

Whisk the powdered sugar, water and corn syrup together until smooth and pourable, like heavy cream; add water a teaspoon at a time if it is too thick.

Divide and tint the icing with food coloring if using, keeping one batch plain if you want a mix of colors.

Pour the icing slowly over each cube, covering the top and sides completely in one pass.

Let the icing set for 20 minutes, then add a small sugar decoration or dragee to the top of each while it is still slightly tacky.

Let the petit fours sit uncovered for at least 1 hour, until the icing is fully set and no longer wet to the touch, before arranging on a stand.