Preheat oven to 350° Grease a 13x9 rectangular pan or a 10 inch round cake pan. Line with parchment paper, grease parchment paper and dust pan with oat fiber.
Arrange berries in single layer in bottom of pan. Sprinkle evenly with erythritol.
Whisk baking blend, oat fiber, baking powder, baking soda, & salt. Set aside.
Using a hand mixer on high, beat melted butter, gentle sweet, vanilla extract, and orange essential oil together until lightened in color, about 3 minutes.
Add eggs one at a time, beating well after each addition, scraping down as necessary.
Add half of dry ingredients and mix well. Add yogurt and orange zest. Mix well. Add remaining dry ingredients and mix together on high speed for 1 minute, scraping bowl down as necessary.
Spread batter evenly over prepared berries in pan, making sure to smooth out top.
Bake for 40-45 minutes or until top is golden brown and toothpick inserted in center comes out clean or with a few crumbs attached.
Place cutting board or desired serving dish immediately over top of cake and flip over. Immediately remove parchment paper, so bottom of cake doesn’t get soggy.
Let cool, and then serve!