In mixing bowl, cream butter, sugar, orange zest and vanilla using paddle. Add eggs 1 at a time, beating well between each and scraping down bowl. Add dry ingredients and mix until incorporated. Add sliced almonds, mixing until blended. Divide in half. On floured surface, form each into a log about 15” long. Bake for 27 minutes at 350ºF. Allow to cool and slice the log into 3/8” thick slices. Place cut side down on a sheetpan and dry in a 350ºF oven for 7 minutes. Cool and place in airtight container.