Preheat the oven to 350 degrees F (175 degrees C). Line the bottom of a 9-inch square baking pan with parchment paper. Grease the sides of the pan.

Blend margarine, sugar, and hot chocolate mix in a bowl using an electric mixer until smooth. Add eggs 1 at a time and beat until well combined.

Combine flour, salt, xanthan gum, and baking soda in a separate bowl. Pour into butter mixture and combine. Add vanilla extract; mix well. Pour in soy milk and stir well. Pour mixture into the prepared baking pan, spreading to all corners.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 20 minutes. Let cool completely, about 30 minutes.

Cut into 16 equal-sized pieces and roll into balls.