Preheat the oven to 350°F. Grease and flour a 9x13-inch baking pan or coat it with baking spray that contains flour.
For the ribbon, stir together 1/2 cup brown sugar, 1 teaspoon cinnamon, and 1/2 cup finely chopped toasted pecans. Set aside.
For the streusel, combine 3/4 cup flour, 1/2 cup brown sugar, 1 teaspoon cinnamon, and 1/4 teaspoon salt. Cut in 6 tablespoons cold butter until coarse crumbs form, then fold in 1/2 cup roughly chopped toasted pecans. Refrigerate while you make the batter.
Beat the 15.25-ounce yellow cake mix, 1 cup sour cream, 1/2 cup buttermilk, 1/2 cup melted butter, 3 eggs, 1 teaspoon vanilla, and optional 1/4 teaspoon almond extract for about 2 minutes, until smooth.
Spread half the batter in the pan. Sprinkle the cinnamon-pecan ribbon evenly over it. Carefully spread the remaining batter on top, then scatter the cold streusel over the surface.
Bake at 350°F for 40 to 45 minutes, until the center is set and a toothpick comes out clean or with a few moist crumbs. Cool at least 20 minutes.
Whisk 1/2 cup powdered sugar with 2 tablespoons maple syrup. Add warm water a few drops at a time only if needed for a pourable glaze. Drizzle over the warm or cooled cake.