Melt butter in a small saucepan over medium heat. Cook until foamy and flecked with brown milk solids, 4 to 6 minutes.

Pour into a small heatproof bowl. Cool slightly then refrigerate until solid, 45 minutes to 1 hour.

Combine oats, flour, sugar and salt in a mixing bowl. Mix cooled butter into oat mixture until combined.

Transfer to a 9-inch pie plate and press mixture evenly across the bottom and up the sides, refrigerating until firm, about 20 minutes.

Preheat oven to 350°F (177°C). Bake crust until lightly golden, about 15 to 18 minutes.

Bring honey to a boil in a medium-size pot over medium heat. Cook until honey is deep reddish-brown, 6 to 8 minutes.

Remove from heat and whisk in butter, sour cream, vanilla and salt.

Whisk cornstarch with yolks in a small bowl, then gradually whisk in ½ cup honey mixture.

Scrape yolk mixture into honey mixture and whisk until uniform.

Pour mixture into prepared crust, splash some over edges to saturate, and bake until edges are set but centre jiggles slightly, 14 to 16 minutes.

Cool completely on a wire rack for 2 to 3 hours and dust with icing sugar before serving.