Whisk sugar and egg yolks together in a saucepan; add milk. Bring to a boil, stirring constantly. Cook for 1 minute. Remove from heat; cover and chill until thickened into a custard, about 1 hour.
Crush 1 pint raspberries into a small saucepan. Add 1/3 cup water; bring to a boil. Strain into a bowl, reserving raspberry juice and discarding seeds. Pour juice into a measuring cup and add enough water to measure 1 cup.
Combine raspberry juice, 3/4 cup white sugar, cornstarch, and salt in the same small saucepan. Bring to a boil, stirring constantly. Cook until thick, about 2 minutes. Cover and chill for 15 to 30 minutes.
Preheat oven to 450 degrees F (230 degrees C).
Unroll pie crust and press against the side and bottom of a 9-inch pie plate. Fold excess crust under and press together to form an edge; flute. Prick bottom and side with fork.
Bake in the preheated oven until light brown, 10 to 12 minutes. Let cool.
Whisk mascarpone cheese into the cooled custard. Pour into the pie crust. Arrange remaining 1 pint raspberries in concentric circles over the custard, starting from the edge. Pour glaze over raspberries. Chill pie until glaze sets, about 2 hours.