Apricot thumbprint cookies

I’ll be honest with you: I made these cookies to use up the apricot jam in my fridge; after making a tart, some small cakes and these cookies I still have some around – I wonder if someone splashed it with water or fed it after midnight... :)Apricot thumbprint cookiesadapted from here180g unsalted butter, softened1 cup + 1 ½ tablespoons (218g) sugar1 ½ teaspoons vanilla extract1 egg2 cups + 2