Make your favorite white cake. Bake entire cake in one 8, 9 or 10” square pan. Cool well.
Cut a thin slice off all sides of cake. If top is uneven, use a bread knife to slice of uneven parts from the top of cake. Cut cake into 1 1/2- 2” squares. Place the cut square on a baking sheet evenly spaced.
Prepare buttercream frosting. Beat sugar and vanilla together in medium sized bowl. Add powdered sugar slowly, blending well with each addition. Start adding milk very slowly until you reach the desired consistency (do not add color yet). Add salt. Frost tops of cake squares (only tops).
In a large bowl, combine glaze ingredients. Beat on low speed just until blended; beat on high until smooth.
Pour glaze evenly over tops and sides of cake squares, allowing excess to drip off. Let dry. Repeat if necessary to thoroughly coat squares.
While petits fours are drying, color the remaining buttercream frosting in small batches whatever colors you would like to decorate the petits fours with.
Cut a small hole in the corner of a pastry or plastic bag; insert desired tip for you decorations and pipe colored buttercream onto petits fours.
For an added touch, place in square petit fours cups from baking supply or online.