If you can remember the Leather & Smoke candle I used to make this is slightly similar but with a birchy twist. 

Small-batch candles hand-poured in my kitchen. With hand-blended clean fragrance oils, paraffin-free soy wax, and a cotton wick. My candles are vegan, paraben-free, and phthalate-free.

Soy Candles & “Frosting”: Frosting is when a white crystalline layer forms on the surface of natural waxes such as soy. This is a natural effect of soy wax and only occurs throughout vegetable waxes. Frosting takes place when the natural wax used to make a candle tries to return to its natural state.

The rough, bumpy tops after burning a soy wax candle are caused when the hot wax in the melt pool cools and solidifies at an inconsistent rate. This is a feature of soy wax. In fact, this is a way to show the candle is indeed made with an 100% all-natural soy wax. It does not affect the performance of the candle.