Put gelatine and water in a small pan and heat gently until dissolved. Add shortening, glucose and glycerine and heat until shortening is just melted. Mix well.
Put sifted sugar in a large bowl and make a well in the centre. Pour warm liquid mixture into the well and mix with your hands to a dough-like consistency.
Transfer to a smooth surface. Knead until smooth and pliable. Add flavouring while kneading. If too stiff, add a few drops of boiling water.
Use immediately or store in an airtight container at room temperature for up to a week. Knead again before rolling out. If storing longer, refrigerate and bring to room temperature before kneading and rolling out.