Preheat the oven to 300F.
To make the glaze, simply whisk the confectioner's sugar with the liquids until smooth.
Beat eggs and sugar until lightened and thick. Add lemon zest, vanilla and salt. Sift in flour and baking powder then add and stir until incorporated. Be careful not to over mix. Pipe into desired rings and bake until light golden brown. Glaze immediately.
To make the custard, place all ingredients into a medium saucepan over medium heat. Cook, whisking constantly, until mixture comes to a boil and thickens, 6 to 8 minutes. Strain custard through a fine mesh strainer. Place plastic wrap on top of custard so it doesn't form a skin. Refrigerate.
When ready, place the custard in a piping bag with the tip of your choice. (I use an 804.) Either 1) stick the bag up the bottom of the cake to fill or 2) use a cylindrical tube to form a hole inside to pipe the custard. Go about 3/4 of the way.
Last touch is a candied cherry on top. I've used an amerena cherry.