Preheat oven to 350°. Line an 8-in. square baking pan with parchment, letting ends extend up sides. In a small bowl, mix flour, brown sugar and salt; cut in butter until crumbly. Stir in pecans.
Press into bottom of prepared pan. Bake until edges just begin to brown, 12-15 minutes. Cool completely on a wire rack.
In a large bowl, beat cream cheese and sugar until smooth. Beat in milk, lemon juice, vanilla and salt. Add egg; beat on low speed just until blended. Pour over crust.
Bake until filling is set, 15-20 minutes. Cool on a wire rack for 1 hour.
For jam, in a small saucepan, mix sugar and cornstarch. Add strawberries, rhubarb and lemon juice. Bring to a boil. Reduce heat; simmer, uncovered, until mixture begins to thicken, 6-8 minutes. Cool completely. Spread over filling. Refrigerate until set, 8 hours or overnight.
Using parchment, carefully remove cheesecake from baking pan. Cut into bars for serving.