📋 Instructions

1. 1Heat the oven and pan — Preheat the oven to 350°F (175°C) and lightly grease a 9-inch (23cm) round or 8-inch square baking pan. Line the bottom with parchment for easy release.
2. 2Whisk the dry ingredients — In a large bowl, whisk together the flour, baking powder, and salt until evenly combined. This spreads the leavener so the cake rises evenly.
3. 3Blend the wet ingredients — In a second bowl, whisk the sugar, eggs, milk, melted butter, vanilla, and lemon zest for about 1 minute, until smooth and slightly pale. The mixture should look glossy with no streaks of egg.
4. 4Fold in the flour — Pour the dry ingredients into the wet and fold gently with a spatula just until no dry flour remains. Stop there, since a few small lumps are fine and overmixing toughens the crumb.
5. 5Add the grapes — Toss the halved grapes with a teaspoon of flour if you like, then fold them into the batter gently. Scrape everything into the prepared pan and smooth the top.
6. 6Sugar the top — Sprinkle the coarse sugar evenly over the batter, leaving a small bare border around the edge. This bakes into a crisp, golden crust.
7. 7Bake until golden — Bake at 350°F (175°C) for 32 to 38 minutes, until the top is golden brown, the edges are bubbling, and a skewer near the center comes out with moist crumbs. Rotate the pan halfway through if your oven browns unevenly.
8. 8Cool before slicing — Set the pan on a rack and cool for 15 minutes, then lift the cake out and cool 10 minutes more. Slice warm, since the grapes will still be soft and juicy.