Answer:
This is difficult to work out without seeing them, but it might be that your proportions are incorrect, you are using too much golden syrup or you are cooking the biscuits at too high a temperature — perhaps your oven needs checking? Whatever the reason, there is nothing more annoying when they have been perfect in the past.

Below is our recipe, why not give that a go — good luck.

Anzac biscuit
makes 36
preparation 15 minutes
cooking 25 minutes

1 cup rolled oats
1 cup plain flour, sifted
1 cup caster sugar
1 cup desiccated coconut
125g butter, chopped
1 tablespoon golden syrup
2 tablespoons boiling water
1 teaspoon bicarbonate of soda

1. Preheat oven to moderately slow, 160C. Lightly grease 4 baking trays.
2. In a medium bowl combine oats, flour, sugar and coconut.
3. In a small pan combine butter and golden syrup. Stir over low heat for 2-3 minutes until melted.
4. In a small jug combine water and soda. Stir into butter mixture. Pour into dry ingredients. Mix well.
5. Roll walnut-sized pieces of mixture into balls. Arrange on prepared trays, leaving 4cm space between each biscuit, to allow for spreading. Press lightly to flatten.
6. Bake for 15-20 minutes until golden. Stand 5 minutes, before transferring to a wire rack to cool.