Heat oven to 350 degrees F. Beat butter and brown sugar in mixer bowl until light and fluffy. Add flour; beat until mixture is crumbly. Stir in pecans.
Reserve 1 cup crumb mixture for topping. Press remaining mixture into bottom of 8-inch square baking pan. Bake 15 minutes until golden. Cool on wire rack.
Beat cream cheese and granulated sugar in mixer bowl until creamy. Beat in egg, milk, lemon juice and vanilla. Spread jelly over crust; pour cream-cheese mixture on top. Sprinkle with reserved crumbs. Bake 35 minutes until cheesecake is set and crumbs are golden. Cool in pan on wire rack. Cut into triangles. (Can be made ahead. Store in airtight containers and freeze up to 1 month.) Makes 32 bars.