You should try the recipe again using an ice-cream churner. The fat in an ice-cream base (usually comes from eggs and cream, in this case from eggs and peanuts) helps keep the water from freezing into a solid block (the fat inhibits the formation of ice crystals causing the mixture to form smaller crystals that we perceive as smooth rather than hard and chunky), but the fat alone isn't enough to get a creamy texture. The mechanical action of a churner will further inhibit the growth of large ice crystals while mixing air into the finished product (air gets trapped as the base freezes and thickens) making the end result less dense/more creamy. Since a custard base will do exactly what your nut-base did if you just put into the freezer, there's a good chance your nut-base will work like ice cream if you churn it. If you want to further inhibit the ice crystals while upping the flavor, you could also add one or two tablespoons of liquor (vodka if you don't want to add flavor, but a dark rum would probably be good here).