In another bowl, whisk together the melted butter, lemon peel, orange juice and zest, until combined. Add the eggs, whisk. Add the yogurt and vanilla, and whisk again.
Add the wet ingredients to the dry ones, mixing together until just combined. Expect the batter to be quite thick, being careful not to over mix. Fill the muffin papers and bake for 5 minutes at 425.
After 5 minutes, leaving the muffins in the oven, reduce the heat to 375 degrees F and bake for 10 - 13 minutes more until the tops are golden brown. (I'd never before heard of or done anything like this, although my girl Sally can certainly be trusted!)