Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom and sides of 15x10x1-inch pan with baking spray with flour.
In large bowl, beat all cake ingredients except liqueur with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour batter into pan.
Bake 22 to 28 minutes or until cake springs back when touched lightly in center. Brush liqueur over top of cake. Cool completely, about 20 minutes. To avoid cake crumbs when adding icing, freeze cake 1 hour before cutting.
In large bowl, beat icing ingredients on low speed until powdered sugar is moistened. Beat on high speed until smooth. If necessary, add 2 to 3 teaspoons more apricot nectar until icing is pourable.
Place cooling rack on cookie sheet or waxed paper to catch icing drips. Cut cake into 9 rows by 6 rows. Working with 6 pieces at a time, remove cake pieces from pan and place on cooling rack. Spoon icing evenly over top and sides of cake pieces, letting icing coat sides. (Icing that drips off can be reused.) Let stand until icing is set, about 2 hours.
Decorate with almonds and orange peel as desired. Store in single layer in airtight plastic container.