Beat the margarine, brown sugar, and 1/2 cup white sugar with an electric mixer in a large bowl until smooth. Beat in the egg and vanilla extract. Mix in the flour 1/2 cup at a time, then stir in salt until just incorporated. Fold in the almonds and poppy seeds; mixing just enough to evenly combine. Divide the dough in half. Roll each into a 12 inch log and wrap with waxed paper. Refrigerate for 3 hours.
Preheat an oven to 325 degrees F (165 degrees C). Coat logs in the remaining 1/2 cup of sugar. Cut the logs into 1/2 inch slices and place on a baking sheet.
Bake in the preheated oven until the cookies begin to brown, 15 to 20 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack.