Preheat oven to 325°F Butter 13x9x2 inch metal baking pan. Blend flour, sugar, and salt in processor. Add butter, 2 tablespoons lime peel, and vanilla; process just until blended and dough forms clumps. Press evenly into prepared baking pan. Pierce dough all over with fork. Using sharp knife, cut dough into 12 inch squares, cutting through dough completely, then cut each square in half on diagonal, forming 24 triangles total.
Bake shortbread until golden brown, crisp around edges, and firm to touch, about 45 minutes. Remove from oven. Using sharp knife, immediately recut shortbread, gently separating triangles. Cool shortbread in pan on rack.
Place white chocolate in small metal bowl. Set bowl over small saucepan of gently simmering water and stir just until chocolate is melted and smooth. Remove bowl from over water. Using fork, drizzle melted chocolate in zigzag pattern over shortbread. Sprinkle evenly with almonds and remaining 1 tablespoon lime peel. Let stand until chocolate sets, about 1 hour.