Preheat oven to 350° with rack in center. Spray 4 x 8-inch slant-sided bread pan (bottom measures 3.5 x 7.5-inches) with nonstick cooking spray. Line pan with two strips of parchment paper, crisscross, so about 1 inch of paper overhangs on all sides of pan. This will keep sides of bread soft and allow for easier removal of baked loaf from pan. Spray one more time with nonstick cooking spray.
In large mixing bowl, whisk eggs until well blended. Add honey, oil, and vinegar, and whisk again until well mixed. In a separate bowl, whisk together Cassava Flour, chia seed, flax seed, baking soda, cream of tartar, and salt. Add flour mixture to egg mixture, and whisk until well combined. Batter will be runny.
Pour batter into loaf pan and bake 35 to 45 minutes, until toothpick inserted near center comes out clean, and bread is pulling away from sides of pan. Cool bread in pan on wire rack for 20 to 30 minutes. Remove bread from pan by lifting out with parchment paper.
Serve warm, room temperature, or toasted.
This bread stays moist for about 3 days; it keeps best wrapped in parchment paper, inside an open plastic bag.
NOTE: Small, slant-sided pan is specified to make the tallest loaf possible. A wider pan will work, but will make a shorter loaf.