Preheat oven to 350 degrees with a rack set in the center.
Make the cake: Place milk and salt in a medium saucepan and bring to a boil over medium-high heat; immediately reduce heat and stir in farina. Cook according to package directions, stirring and adjusting heat as necessary, until thickened. Remove from heat and stir in sugar and vanilla; let stand until cooled slightly, about 15 minutes.
Make the caramel: Place an 8-inch round cake pan in oven to preheat. Place sugar, 1/4 cup water, and lemon juice in a small skillet or saucepan over high heat. Stir until sugar is moist and bring to a boil. As sugar begins to caramelize, carefully swirl pan to heat sugar evenly. Cook until sugar begins to turn dark amber in color, about 5 minutes. Remove cake pan from oven and pour caramel into pan, tilting pan to evenly coat; set aside.
Stir eggs and raisins into farina mixture and pour into prepared cake pan. Transfer to oven and bake until firm, puffed up, and a knife inserted into the center comes out clean, 25 to 35 minutes.
Invert a rimmed serving plate over cake pan and, working carefully (caramel will be very hot), turn pan over onto plate and lift it off; caramel will run down the sides of the cake. Let cake cool to room temperature before serving.