Preheat and prep: Heat your oven to 350°F (175°C). Lightly grease an 8-inch square pan or a 9-inch round pan, and line the bottom with parchment for easy removal.

Make the vegan “buttermilk”: In a measuring cup, stir 1 cup non-dairy milk with 1 teaspoon apple cider vinegar. Let it sit for 5 minutes to lightly thicken.

Mix the dry ingredients: In a large bowl, whisk 2 cups all-purpose flour, 2 teaspoons baking powder, 1/2 teaspoon fine sea salt, and 1 teaspoon ground cinnamon.

Whisk the wet ingredients: To the “buttermilk,” add 1/2 cup sugar (or 1/3 cup sugar + 2 tablespoons brown sugar), 1/3 cup neutral oil, and 1 1/2 teaspoons vanilla. Whisk until smooth.

Combine: Pour wet into dry. Stir gently with a spatula until just combined. Do not overmix; a few small lumps are fine.

Make the streusel: In a small bowl, combine 1/2 cup brown sugar, 2/3 cup flour, 1 1/2 teaspoons cinnamon, and a pinch of salt. Add 1/4 cup melted vegan butter (or softened) and mix with a fork until crumbly. If it looks dry, add 1–2 teaspoons more melted butter.

Layer the cake: Spread half the batter into the pan. Sprinkle about one-third of the streusel over it. Gently spread the remaining batter on top, then finish with the remaining streusel. Lightly press the crumbs so they adhere.

Bake: Bake for 32–40 minutes, depending on your pan. The cake is done when a toothpick inserted in the center comes out clean or with a few moist crumbs, and the top is golden.

Cool: Let the cake cool in the pan for at least 20 minutes. This helps it set and slice cleanly.

Optional glaze: Whisk 1/2 cup powdered sugar with 1–2 teaspoons non-dairy milk and a few drops of vanilla until pourable. Drizzle over the cooled cake.