One hour ahead, set out eggs and butter to come to room temperature.
Pre-heat oven to 350°.
Grease a 9x5 loaf pan with butter or oil-flour spray and set aside.
Beat together softened butter, sugar, and both zests until light and fluffy. I did this for a full five minutes in a stand mixer. If not available, use a hand mixer or even a whisk. But take the time. You'll be glad you did.
In a bowl, whisk flour, baking powder, and salt to combine. Then fold the dry stuff into the wet stuff—making sure to scrape up the bits at the bottom of the bowl— until the dry just barely disappears. Don't go beyond this or you'll overmix and you know what that means—a tough crumb. Horrors!
Use the silicone spatula (It was made for jobs like this.) to scrape the batter into your loaf pan. Shake the pan gently, back and forth and sideways, to get the batter evenly distributed. Bake in the center of the oven for 55 minutes, turning the pan around half-way through.
Remove from oven and test for doneness. I use my digital thermometer and look for a temp of 200-205°. The toothpick test works, too.
Set the loaf pan on a wire rack for ten minutes, then turn it over (careful, it's hot) to remove the loaf. It should drop right out into your towel-protected hand. Return the loaf to the wire rack.
Now, for the glaze. In a small sauce pan over medium-low heat, whisk together 1/3 cup marmalade, powdered sugar, and 1/2 tbsp butter. When fully melted and combined, pour the glaze carefully over the loaf. You may want to put a sheet pan under the loaf to catch any drips. Smooth the glaze evenly over the loaf with the back of a large spoon or offset spatula. It's great if some of the glaze drips down the sides.
Let the loaf cool for about an hour before slicing.
Make tea. Find a friend to share.