In a large bowl, beat butter with an electric mixer until creamy.
Sift powdered sugar; gradually add to butter, beating until mixture is light and fluffy. Beat in eggs, 1 at a time, beating well after each addition.
Beat in vanilla. Gradually beat flour into creamed mixture.
Heavily butter a 10-inch (12-cup) plain or decorative tube pan; add sliced almonds (if used), then tilt pan to coat inside surfaces with nuts. Or butter pan and dust with flour.
Scrape batter into pan and smooth top surface.
Bake in a 300° oven until a slender wooden toothpick inserted in center come out clean, about 1½ hours.
Let cool in pan on a rack for about 5 minutes; run a knife around edges of tube to loosen center of cake, then invert cake onto rack to cool.
Serve warm or cool, cut into thin slices.
Note: If made ahead, store airtight for up to 2 days.