Preheat oven to 350°F (175°C). Lightly butter a 9-inch round cake pan (or 8x8 square) and line the bottom with parchment paper for easy removal. Brush melted butter along the sides.

Combine dry ingredients

In a large mixing bowl, whisk together 2.5 cups all-purpose flour, 0.75 cup granulated sugar, 2 tsp baking powder, and 0.5 tsp fine sea salt until evenly distributed.

Mix wet ingredients

In a separate bowl, whisk together 0.5 cup melted butter, 1 cup whole milk, 2 large eggs, 1 tsp vanilla extract, 1 cup ripe peach purée, and 0.25 tsp peach extract (if using) until smooth and homogenous.

Combine wet and dry

Make a well in the center of the dry ingredients and pour in the wet mixture. Gently fold with a spatula until just combined — the batter should be smooth with no large streaks of flour. Do not overmix to keep the cake tender.

Adjust consistency

If the batter seems very thick, add up to 1–2 tbsp milk to reach a pourable but thick cake-batter consistency. Scrape batter into the prepared pan and level the top gently with an offset spatula.

Peach Swirl

Cook peach compote

Combine 2 cups diced fresh peaches, 3 tbs granulated sugar, and 1 tbs lemon juice in a small saucepan over medium heat. Stir frequently and bring to a gentle simmer until the peaches release juices, about 6–8 minutes.

Thicken

Mix 1 tsp cornstarch with 1 tsp water to make a slurry, then stir it into the simmering peaches. Cook 1–2 more minutes until the mixture thickens slightly and becomes glossy. Remove from heat and let cool 5–10 minutes.

Create swirl

Drop 6–8 tablespoons of the warm (not hot) peach compote in dollops across the top of the batter in the pan. Using a butter knife or skewer, swirl the compote gently through the batter in a loose figure-eight or circular motion to create a marbled pattern. Avoid over-swiring; distinct peach ribbons should remain.

Bake

Bake in the preheated 350°F (175°C) oven for 28–36 minutes until the top is golden and a toothpick inserted into the center (avoiding the peach swirls) comes out with a few moist crumbs but not wet batter. Rotate the pan halfway through baking for even color. If using a darker pan, reduce time by 3–5 minutes and check earlier.

Once baked, remove the cake from the oven and allow it to cool in the pan on a wire rack for 10–15 minutes. Run a knife around the edge, then invert onto the rack, peel off parchment, and right the cake onto the rack to cool completely (about 45–60 minutes) before glazing.

Peach Glaze & Finish

Make the glaze

Whisk together 1.5 cups powdered sugar, 3 tbs peach purée, 1 tbs milk or cream, 0.25 tsp vanilla extract, and a pinch (0.25 tsp) salt in a small bowl until smooth and pourable. If too thick, add milk 1/4 tsp at a time; if too thin, add a little more powdered sugar.

Glaze the cake

Place the cooled cake on a serving plate or rack with a tray beneath to catch drips. Spoon the glaze over the center and gently push it outward to create a thin, even coating. Allow glaze to set for 10–15 minutes.

Garnish

Brush the cake rim lightly with 1 tbs melted butter (optional) and sprinkle 2 tbs coarse sugar around the edge if you like sparkle. Top with 1/2 cup thin peach slices and arrange fresh mint leaves as desired. Chill briefly (10–15 minutes) if you want a firmer glaze before serving.