1. Combine strawberries and 1 tablespoon sugar in a small bowl. Set aside.
2. Combine port and 1/4 cup sugar in a small saucepan over medium-high heat. Bring to a boil; cook 7 minutes or until slightly thickened. Stir in rhubarb; cook 7 minutes.
3. Bring 3 1/2 cups water to a simmer in a small saucepan (do not boil). Keep warm over low heat. Combine milk, remaining 1/2 cup sugar, salt, and nutmeg in a separate saucepan; bring to a simmer (do not boil). Keep warm over low heat. Melt butter in a large Dutch oven. Add rice to pan; cook 1 minute, stirring constantly. Stir in 1 cup hot water; cook 3 minutes or until liquid is nearly absorbed, stirring constantly. Add remaining water, 1/2 cup at a time, stirring constantly until each portion of water is absorbed before adding the next. Add milk mixture, 1/2 cup at a time, stirring constantly until each portion of milk is absorbed before adding the next (about 30 minutes total). Stir in vanilla; cook 1 minute. Remove from heat; stir in mascarpone until cheese melts. Place about 1/2 cup risotto in each of 8 bowls. Top each serving with 2 tablespoons port mixture and 1/4 cup strawberry mixture.