Place parchment paper on a pie dish (with a properly-sealed bottom, or preferably an oven-safe glassware for pie baking).

Turn on the oven on 350F/ 170C (Convection is preferred).

In a small microwave-safe bowl, place the butter, sugar & Agava and microwave it for 60 seconds. Mix well for about 2 minutes until the butter is completely dissolved and the mixture is consistent and smooth.

Pour the mixture onto the pan, and spread evenly across the surface.

Cut the nectarines into about 0.2'' slices (see picture above) and organize them in an orderly manner so they form the shape as in the picture.

Now make the dough mixture -

In a microwave-safe mixing bowl, place the butter & sugar, and microwave for 60 seconds. Mix well and add the vanilla extract, maple syrup, apple sauce, 1 cup of milk and vinegar. Mix well again.

In a separate bowl, mix the flax seed meal & 1.7 oz milk for 30 seconds to get a consistent thick mixture. Add it to the rest of the ingredients and mix well.

Finally mix the flours together with the baking soda and baking powder, and add them to the mixture.

Pour the mixture on top of the nectarines, and immediately place the pan in the oven.

Set the timer for 30 minutes and check if the cake seems stable and slightly brownish on the top (briefly and gently press in the middle to check stability).

Remove from the oven and let it cool for an hour.

Attach a flat dish to the top of the pie, and carefully but rapidly turn the pie upside down, so that the bottom is now the top of the cake.

Serve at room temperature or cold.