Cake – What are the pips and skin of an orange

I'm from the garden/landscape section of the site, but post your question there anyway, regardless of my answer - you may get a better/different one! Navel oranges, technically, are parthenocopic, which means they produce fruit without fertilisation, and that's why they are seedless. However, if the blossom is pollinated by a suitable donor, then seeds may form. These are usually, as you've discovered, vestigial seeds and may not even be fertile. The cause of the pollination (if the fruit is grown in the States, usually) is beekeepers bringing bees to orchards where other varieties of orange may be growing, or other varieties growing too close to parthenocopic varieties, usually out of ignorance by the grower when planting. Quite often, the navel fruits with seeds are of a smaller size, though not always.

First I would recommend viewing the episode of Good Eats, Orange Aid. While there is not a direct answer to your question Alton does talk about getting the maximum orange flavor as well as how to avoid the pithy flavor. (This link to Orange Aid will take you to Amazon Prime, where if you are not an Amazon Prime member you may purchase for $2.99...)

The take away that I believe applies to your situation is this: remove as much of the pith as possible (but I'm guessing you already know this)...

The second take away is that the variety of orange really matters, many varieties are more flavorful than others and these are NOT the varieties most frequently found in your mega-mart. (which are chosen more for appearance than flavor--go figure) Valencia, Hamlin and/or Seville oranges would be good choices. Avoid NAVEL ORANGES!

Having looked at your recipe ever so briefly I might suggest an experiment as well... take about an ounce of vodka or everclear and let that sit for a few days with orange zest and vanilla beans, filter out the solid and use this concoction in place of the vanilla extract. The orange oils in the zest are alcohol soluble and thus should provide you with a nice orange extract to intensify your flavor. (I have not tried this with orange, so this is pure speculation).