Stir ½ tablespoon sugar, the lemon juice, vanilla, and cinnamon into the peaches, then set the ramekin aside.
Make the topping
In a small bowl, whisk together the flour, 1½ tablespoons sugar, and baking powder.
Pour in the milk and whisk until the batter is smooth.
Pour the batter evenly over the peaches.
Set the ramekin on a baking sheet to catch any drips.
Bake for 25 to 28 minutes, until the topping is golden brown and the peach juices bubble around the edge.
Serve warm, on its own or with vanilla ice cream or whipped cream.
Notes
Use ripe peaches. A ripe peach gives slightly when you press it and smells sweet at the stem. Ripe fruit makes the best filling, but avoid peaches that are squishy or bruised, since overly soft fruit releases too much juice and can leave the topping wet.Don't overbake. Pull the cobbler once the topping is golden and the juices bubble around the edge, usually 25 to 28 minutes. Leaving it in too long dries the topping out and bakes it hard, so start checking at 25 minutes.Use the right ramekin. This one serving peach cobbler is built for a 10-ounce ramekin. Too small and it overflows, too large and the topping spreads thin and bakes dry. To check yours, fill it with water and measure the volume.Slice the peaches evenly. Cut the peach into ¼-inch slices so the fruit cooks at the same rate and you don't get firm pieces next to soft ones.If doubling the recipe, bake in either two 10-ounce ramekins or one 5x5-inch baking dish.