Preheat and prep. Heat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with a strip of parchment that overhangs the long sides for easy lifting.

Make the cinnamon swirl. In a small bowl, mix 1/3 cup granulated sugar, 1/3 cup brown sugar, and 1 tablespoon ground cinnamon. Set aside.

Combine dry ingredients. In a medium bowl, whisk 2 cups all-purpose flour, 2 teaspoons baking powder, and 1/2 teaspoon salt. This helps the loaf rise evenly.

Cream butter and sugar. In a large bowl, beat 1/2 cup (1 stick) softened unsalted butter with 3/4 cup granulated sugar until light and fluffy, about 2 minutes. This traps air and makes the loaf soft.

Add eggs and vanilla. Beat in 2 large eggs, one at a time, scraping the bowl as needed. Mix in 1 1/2 teaspoons vanilla extract until smooth.

Alternate dry ingredients and milk. Add half the flour mixture, then 3/4 cup milk, then the remaining flour. Mix on low just until combined. Do not overmix or the loaf can become dense.

Layer and swirl. Pour half the batter into the pan and smooth the top. Sprinkle on half the cinnamon-sugar mixture. Add the remaining batter, smooth again, and finish with the rest of the cinnamon sugar. Use a butter knife to gently swirl in a few figure-eights. Don’t over-swirl—you want distinct ribbons.

Bake. Bake for 48–58 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. If the top is browning too quickly, tent loosely with foil for the last 10 minutes.

Cool. Let the loaf cool in the pan for 15 minutes, then lift it out and cool completely on a wire rack. This helps set the crumb and prevents a gummy texture.

Glaze (optional but lovely). Whisk 3/4 cup powdered sugar with 1–2 tablespoons milk or cream and 1/4 teaspoon vanilla until smooth and pourable. Drizzle over the cooled loaf. Let it set for 10 minutes before slicing.

Slice and enjoy. Cut into 10–12 slices. Serve slightly warm or at room temperature with coffee or tea.