In a small pot, over low heat melt 1/4 cup of butter, remove from heat and set aside.
In your food processor, fitted with dough blade (or stand mixture with dough hook) combine 2 1/2 cups cassava flour, 1/2 cup room temperature butter, sea salt, yogurt, and water. Process until a smooth dough is formed. If it is too dry add more water 1 teaspoon at a time or if it is too wet add additional cassava flour 1 tablespoon at a time. Do not worry you cannot over work this dough.
Divide dough into 4 equal portions. Roll out one portion on a surface generously dusted with cassava flour until 1/8 inch thick.
Cut into desired shapes using biscuit, cookie cutter, sharp knife or pizza cutter. Arrange crackers on a parchment paper lined baking sheet, leaving at least 1/4 inch between crackers. Prick each cracker using a fork (to avoid puffing) and gently brush melted butter. If desired, lightly salt the tops of the buttered crackers.
Bake at 400 on a middle oven rack for 6-8 minutes or until lightly brown and crispy. (I suggest turning your rack after the first 4 minutes of baking)
Transfer baked crackers to a cooling rack, they will get crispier as they cool.
Notes
Crackers that are thinner will start to brown. Adjust cooking time according to the thickness of your crackers.