Heat the oven to 350°F (175°C). Thoroughly grease and flour a 10- to 12-cup Bundt pan, taking care to coat the center tube and every decorative crevice.

Combine the streusel flour, brown sugar, cinnamon, and salt. Rub in the butter until coarse crumbs form, then stir in the chopped pecans or walnuts if using; chill for 10–15 minutes for a more defined filling.

Whisk the cake flour, baking soda, baking powder, salt, cinnamon, ginger, nutmeg, and cloves in a medium bowl. In a separate large bowl, whisk the oil and granulated sugar.

Add the eggs to the oil mixture one at a time, whisking after each addition. Whisk in the pumpkin purée and vanilla until the mixture looks evenly blended.

Add the dry ingredients in three additions, alternating with the buttermilk. Mix only until incorporated so the finished cake remains soft rather than dense.

Spoon about half of the batter into the prepared Bundt pan. Sprinkle the streusel in an even ring through the center, keeping it away from both the outer wall and inner tube.

Cover the filling with the remaining batter and smooth the top gently. Bake for approximately 55–70 minutes, until a skewer inserted into the cake comes out clean or with a few moist crumbs; avoid testing directly through the streusel.

Cool the cake in the pan for 15–20 minutes, then invert it onto a wire rack. Let it cool completely, for at least 1 hour before glazing.

Whisk the confectioners' sugar, 1 tablespoon of milk, cream, or maple syrup, vanilla, and optional salt until smooth. Add the second tablespoon of liquid only if needed, then drizzle the glaze over the cooled cake.