Preheat oven to 350°. Lightly grease a 13x9-inch baking pan and line with parchment paper.
In a stand mixer bowl, cream together 1 cup butter and the brown sugar. Beat in eggs and 2 teaspoons vanilla.
In a separate bowl, combine the flour, cardamom, baking soda, and 1 teaspoon salt; stir in the oats.
Add dry ingredients to the creamed mixture and mix until well blended.
Pat about ¾ of the oat mixture into the bottom of the prepared baking pan, setting the rest aside.
In a heavy saucepan over low heat, combine the condensed milk, chocolate chips, 2 tablespoons butter and ½ teaspoon salt. Stir until the chocolate is melted and the mixture is smooth. Stir in the 2 teaspoons vanilla and hazelnuts.
Spread the chocolate mixture over the unbaked oat crust in the baking pan. Crumble the remaining oat mix evenly over the top.
Bake for 20-22 minutes until golden brown and firm—do not overbake. Cool completely and cut into squares.