Melt the chocolate in microwave, stirring several times while melting. Set aside.
Combine flour, cocoa powder, baking powder, salt and gjetost, being careful not to let the gjetost clump. Set aside.
Cream butter with sugar and corn syrup in a stand mixer with a paddle attachment.
Scrape down and add vanilla extract and eggs one at a time. Mix until fully incorporated.
While mixer is running, stream in melted chocolate.
Add dry ingredients and mix until just combined.
Scoop into portions and chill for 3 hours. Roll in powdered sugar before baking.
Bake at 350°F for 12-15 minutes, until cracked looking and just firm.