I bake them in a 350 degree oven for 45 minutes but it seems the insides refuses to harden and dry any advice?   PS: The mixture is (oat flour, baking powder, mashed banana, Jam, milk, maple syrup, honey, vanilla extract, nuts)  Thanks 
Making your own sugar syrup should work.  Corn syrup can be replaced by a sugar syrup. Combine one cup of pure cane sugar with 1/4 cup of water and heat over a low flame. Cool and use directly in a recipe. If preferred, cover the pan for three minutes to help remove sugar crystals, then add 1/4 teaspoon of lemon juice or cream of tartar to the pan and stir frequently until it reaches the soft ball stage (a drop of the syrup will form a ball when immersed in cold water). Cool and store in a sealed container at room temperature. It should keep for up to two months. Alternatively, add granulated or brown sugar to a recipe that calls for corn syrup, cup for cup, then increase the amount of liquids used in the recipe by 1/4 of the amount of sugar added.  For your use, you'll probably want the liquid version. 