Soften butter and whip it
Mix in corn starch, icing sugar, and all purpose flour until well combined
If adding Toblerone or chocolate, wrap dough in Saran wrap and chill for 20 minutes to harden
Press dough into a parchment-lined 8x8 pan and tamp down evenly
Bake at 325°F for 30 minutes until edges are slightly brown
Cool for 10-15 minutes before cutting to prevent cracking
Cut into bars or desired shapes and serve
