1. Preheat oven to 350°. Spray ramekins with cooking spray. Cut 12 parchment paper circles to fit ramekins; set 1 in each.
2. Bring brown sugar, 1/2 cup granulated sugar, and 1 cup water to a simmer in a large frying pan and cook until reduced slightly and sugar has dissolved, about 5 minutes. Turn off heat and submerge lemon slices in syrup. Let sit, turning occasionally, until rind and pith have begun to turn translucent, 20 to 30 minutes.
3. Beat oil, lemon zest and juice, vanilla, salt, eggs, remaining sugar, and limoncello in a bowl with a mixer on medium speed until well blended.
4. Whisk together flour, cornmeal, baking powder, and baking soda in a medium bowl. Gradually add to wet mixture and beat on medium speed until just blended. Stir in pine nuts.
5. Pour 1 tbsp. syrup from lemon slices into each ramekin. Using tongs, remove lemon slices from syrup and put one in each ramekin; reserve remaining syrup. Evenly divide batter among ramekins and set on a rimmed baking pan.
6. Bake until a toothpick inserted in centers comes out clean, about 25 minutes. Let cool on a rack 10 minutes, then run a small, thin knife or spatula between cakes and ramekin edges and invert cakes onto plates or a platter. Remove parchment from cakes and brush with more syrup if you like.
Note: Nutritional analysis is per cake.