Preheat the oven to 350°F (175°C). Grease and fully line a 9x5-inch loaf pan with parchment paper.

In a medium bowl, whisk together the flour, granulated sugar, brown sugar, and salt for the streusel. Add the cold plant butter and vanilla bean paste. Work together with your fingertips until a mixture of fine crumbs and large buttery clusters forms. Refrigerate while preparing the batter.

In a large bowl, whisk together the granulated sugar, brown sugar, oil, yogurt, milk, vanilla bean paste, maple emulsion, butter extract, and apple cider vinegar until completely smooth.

Add the flour, cornstarch, baking powder, baking soda, salt, cinnamon, and nutmeg. Whisk just until combined and no dry streaks remain.

Spread just under half of the batter into the prepared loaf pan.

Sprinkle half of the chilled streusel evenly over the batter.

Carefully spread the remaining batter over the streusel until completely covered.

Sprinkle the remaining streusel evenly over the top, leaving plenty of large buttery clusters.

Sprinkle the top lightly and evenly with coarse sanding sugar just before baking.

Bake for 55–65 minutes, or possibly longer if your oven runs slower. Check the loaf at 45 minutes and tent loosely with foil if the streusel is browning quickly. The loaf is done when the center reaches 200–203°F (93–95°C), the center no longer jiggles, and a tester inserted into the cake portion comes out with moist crumbs but no wet batter.

Cool in the pan for 10–15 minutes, then carefully lift the loaf onto a wire rack.

While the loaf is still slightly warm, whisk together the powdered sugar, milk, vanilla bean paste, maple emulsion, and salt until smooth and pourable. Spread the glaze evenly over the top, allowing it to naturally drip down the sides.

Immediately sprinkle lightly with Maldon flaky sea salt while the glaze is still wet.

Allow the glaze to set on the counter for 3–4 hours, or refrigerate the loaf for about 30 minutes for set glaze with a still-warm center. Serve warm or fully chilled.