Preheat oven to 350 degrees F (175 degrees C). Spray with baking spray or grease and flour a 9x5-inch loaf pan.
Mix Whey Low Golden or brown sugar and cinnamon together in a bowl.
Beat Whey Low Granular or white sugar and butter together in a bowl using an electric mixer until smooth and creamy. Beat in eggs, 1 at a time, until incorporated; add vanilla extract.
Combine flour and baking powder together in a bowl; stir into creamed butter mixture. Mix the skim milk into batter until smooth. Pour half the batter into the prepared loaf pan; add half the apples and half the brown sugar mixture. Lightly pat apple mixture into batter. Pour the remaining batter over apple layer; top with remaining apples and brown sugar mixture. Lightly pat apples into batter; swirl brown sugar mixture through apples using a spoon.
Bake in the preheated oven until a toothpick inserted in the center of the loaf comes out clean, 50 to 60 minutes.
To make the vanilla glaze, mix all ingredients together in a small bowl. Drizzle on top of cake.
Dice the apples so they are small and all about the same size and there are no big chunks of apples. Dicing them gets them to be just the right size and allows them to cook evenly.
Divide Evenly. When dividing the batter, try your best to place half the batter on the bottom layer so the apple cinnamon swirl will be in the center of the cake. If you layer too little, the apple cinnamon swirl will be very low near the bottom. If you place more than half, then the cinnamon apple swirl will be near the top.
Give it a swirl. Just before going in the oven, I like to take a knife and swirl the apple cinnamon mixture. This is completely optional, but it kind of stirs it up a little more and will hopefully provide a nice presentation.