Pre-heat oven to 350° with rack in the center of the oven.
Make the filling first by creaming together sugar and cream cheese in the bowl of a stand mixer. Add the vanilla, spices and egg yolk; mix for about 1 minute, until smooth and creamy. Put in a pastry bag or medium zip lock and set aside.
Put all muffin ingredients together in a large bowl and mix until smooth. Fill muffin tin with paper liners and spray. Fill 12 muffins cups 2/3 full, you may have some batter left over, to cook in a separate pan. Bake 15 minutes and remove pan from oven.
Cut the tip off pastry bag to about ½” wide. Put cut end in center of each partially baked muffin, squeeze lightly while pulling up and make a circular motion with the filling that comes out of the top of the muffin dough. It will stick up a bit, but after cooking, it may fall and leave a bit of a hole. Bake another 15 minutes or so. Check with a toothpick inserted into the muffin (not the cream cheese) for a clean or crumbly result (should not be wet).
Cool on a rack until cream cheese is set (or you can’t wait any longer). Refrigerate if not eating within a couple of hours.
Chef’s Note: The cream cheese center has a tendency to fall after cooking. Use jumbo paper cups, still filling only 2/3 full and the extra paper seems to give the muffins some extra strength to the very soft crumb of the muffin.
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