In Section 2.2 of the paper cited, the method and solvent are specified:
"...soybean wax suspension was prepared through mixture of 1 g of soybean wax and 50 mL ethanol solution followed by heating at 65º C for 3 min." The superhydrophobic character of the coating described in the paper may not be necessary for the tart shell (see below for examples). Extra care must be observed when following this recipe, for the flash point of ethanol is only 14º C, but this method has the advantage of easy evaporation and safe consumption of the carrier solvent.
Edible waxes can be emulsified and dispersed in water and are widely used to coat fruit and vegetables. Spraying an aqueous solution onto a tart shell could be adjusted so as not to overwet the shell, but some experimentation will be necessary. Wax emulsions are commercially available from many sources, such as Hexion (Ref 1) and Lubrizol (Ref 2). More commercial sources are listed in Ref 3.
Or, with a bit of experimentation, a food-grade wax (e.g., carnauba or polyethylene) and a food-grade emulsifier can be emulsified with intense stirring in hot water (to melt the wax), then cooled to stabilize the formulation.
Cooking and baking are specialized branches of chemistry, but you can eat your mistakes.
Ref 1. https://www.hexion.com/en-US/chemistry/wax-emulsions
Ref 2. https://www.lubrizol.com/-/media/Lubrizol/Coatings/Coatings-Literature/Wax-Additives-Product-Guide---22-122162.pdf
Ref 3. https://www.thomasnet.com/products/fruit-vegetable-coating-wax-93060200-1.html