Make the syrup by combining sugar, water, and lemon juice in a saucepan. Place over medium heat and bring to boil, stirring occasionally. Reduce heat and simmer for 5 minutes. Allow to cool and then refrigerate until very cold.
Preheat the oven to 180°C/350°F. Line two baking trays with baking paper.
Sift the flour, baking powder, and salt.
In a bowl beat butter until smooth and creamy. I used a stand mixer but beating with a wooden spoon is fine. Beat in the sugar until fluffy. Beat in the egg and egg yolk followed by the yogurt and vanilla. If the mixture looks curdled that's not a problem. Gradually stir in the dry ingredients.
Divide the dough into 16 equal portions.
Roll into balls and arrange on baking trays. Flatten slightly and press an almond into the centre. Bake for 30 minutes until golden brown.
As soon as they come out of the oven transfer the cookies baking dish with high sides to catch the syrup. Immediately pour the cold syrup onto the hot cookies. After 5 minutes turn the cookies over and then again a few more times. I never got all the syrup to absorb into the cookies but maybe the cookies were a little overbaked.
Store the cookies in a sealed container in the refrigerator and they will continue to absorb the syrup and develop flavour. Enjoy with a strong espresso!