Preheat the oven to 180°C (350°F/Gas 4). Grease a deep 20cm (8inch) round cake tin and line with baking paper.
Sift the flour into a bowl and add the almonds and poppy seeds. Make a well in the centre.
Place the butter, sugar, jam, orange zest and juice in a saucepan. Stir over low heat until the butter has melted and the mixture is smooth. Gradually add the butter mixture to the dry ingredients, whisking until smooth. Add the egg and whisk until combined. Pour into the tin and bake for 50–60 minutes, or until a skewer inserted into the centre of the cake comes out clean. Leave in the tin for 10 minutes, then turn out onto a wire rack to cool.
Spread the icing over the cooled cake. Decorate with strips of orange zest, if desired.