Preheat your oven to 325°F (165°C). Generously grease and flour a 10-inch bundt pan, taking extra care to reach all the nooks and crannies.
In a medium bowl, whisk together flour, baking soda, salt, cinnamon, nutmeg, and allspice until evenly combined.
Peel, core, and chop your apples into ½-inch pieces. Toss your chopped apples with 1 tablespoon of the flour mixture to prevent them from sinking during baking.
In a large bowl, beat oil and sugar with an electric mixer on medium-high speed for 2-3 minutes until well combined and slightly lighter in color.
Add eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Gradually add the flour mixture to the wet ingredients, mixing on low speed just until combined. Don't overmix.
Using a rubber spatula, gently fold in the prepared apples and nuts if using.
Pour the batter into your prepared bundt pan, smoothing the top with a spatula. Bake for 60-65 minutes, or until a wooden pick inserted in the center comes out clean.
Allow the cake to cool in the pan for exactly 15 minutes. Invert onto a cooling rack and let cool completely before glazing.
For the glaze: In a medium saucepan over medium heat, melt butter. Add brown sugar and stir until dissolved, about 2 minutes.
Add milk, bring to a boil, and cook for 1 minute, stirring constantly. Remove from heat and stir in vanilla and salt. Let cool for 5 minutes.
Gradually whisk powdered sugar into the warm caramel until smooth and pourable. If too thick, add a teaspoon of milk; if too thin, add more powdered sugar.
Pour the warm glaze over your cooled cake, allowing it to cascade down the sides naturally. For a professionally finished look, glaze in two layers, allowing the first to set for 10 minutes before adding the second.