Preheat oven to 400 degrees. Lightly spray five 4-inch silicone hamburger bun molds or line a baking sheet with parchment paper and set aside. In a small bowl stir together 26 grams (1/4 cup) of the flaxseed meal and the water until fully combined
Set the flax/water mixture aside and let sit at least 10 minutes or until gummy in texture. While the mixture is sitting, sift the remaining dry ingredients into a large mixing bowl until there are no lumps.
Stir the butter, plain yogurt and vinegar in until fully combined. After the flax/water mixture has set for 10 minutes, pour the gummy mixture into the dough. Sprinkle in the xanthan gum and stir for at least 30 to 40 seconds or until a smooth dough forms.
Scrape down the sides of the bowl and push the dough to the center of the bowl. Allow the dough to sit for 10 minutes to absorb and bind together. After 10 minutes check your dough. The dough should be moist and lightly sticky.
Divide the dough into 5 equal portions. Roll each portion into a smooth tight ball. Press each portion into the prepared hamburger molds. If using a baking sheet form the ball into a 4-inch wide hamburger bun shape.
For a darker top brush the tops of the buns with melted butter or egg wash. If desired top the egg wash or butter with desired amount of sesame seeds. If using the seeds use the back of a measuring cup and gently press the seeds into the butter or egg wash
Place in the preheated oven. Bake at 400 degrees for 25 minutes or until golden and a tester comes out clean. remove from the oven and allow to cool on the pan in the molds for 20 minutes until firm.
Remove from the molds/baking sheet. Transfer to a wire rack and cool completely before slicing. Once cooled, turn the buns on their sides. Use a sharp knife and cut the buns in half to create a top and bottom bun
Use immediately or store in airtight container at room temperature up to 3 days. Can also store in the freezer up to 3 months.