Preheat oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan or line with parchment paper.
In a large bowl, whisk together flour, sugar, baking powder, apple pie spice, and salt.
In a separate bowl, mix apple cider, egg, melted butter, and vanilla until smooth.
Add wet ingredients to dry and stir gently until just combined—do not overmix.
Pour the batter into the prepared pan and smooth the top.
Bake for 50–60 minutes or until a toothpick inserted in the center comes out clean.
While baking, mix the topping ingredients in a small bowl.
Immediately after baking, brush topping mixture over the warm loaf.
Cool in the pan for 15 minutes, then transfer to a wire rack to cool fully before slicing.