Alrighty, finished up.
This is the Grapefruit and White Chocolate Cake from Snacking Cakes, which lots of folks here have baked before, I am very late to the party.
It’s an oil and yogurt citrus cake with grapefruit as the citrus and white chocolate to offset the bitterness. The yogurt gives it a softer texture than the orange olive oil cakes I often bake.
One thing I haven’t encountered in a while - the cake sank as it cooled. Not concave, but from nicely domed to flat. It last happened the first time I baked an orange olive oil cake, and my fix was to drop the temperature to 325 (vs the 375 of that recipe) - never happened again. So I’m wondering why it happened today. So far my theories are that the batter is very rich because of the whole milk yogurt plus oil plus chocolate chips.
One day I’ll learn to make a glaze look pretty 
The tester I made is delicious (even though the chocolate chips sank in that tiny portion)! I hope my friend’s parents, for whom the loaf is intended, will enjoy it!
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