Thanks for trying out my recipe! Malt syrup is Barley Malt Syrup. It adds sweetness to the bread since beer can be a little bitter, while contributing a little to the beer flavor. It also contributes to the browning of the bread. It's made from Organic Sprouted Barley and is a thick syrup often found in the sugar area of the grocery store. Substitutes for it can be either honey or molasses on a one for one basis. In terms of strength of flavor, Barley Malt Syrup is maybe half way between honey and molasses. Since the recipe only calls for a couple teaspoons, you can also just substitute with sugar on a one for one basis. Hope this helps! Good luck with it; I love to hear how it turns out!

http://www.foodsubs.com/Syrups.html
I've read an acceptable substitute is combine 0.5 L dark beer with 500 g sugar and boil it to a syrup, but have never tried it.