In the bowl of a stand mixer, whisk together warm milk and yeast by hand, and let stand until foamy, 5 to 10 minutes.

Add brown sugar, Browned Butter, eggs, orange zest, and vanilla to yeast mixture. Using the paddle attachment, beat at medium speed until combined. Add 2 cups (250 grams) flour and salt, and beat until a shiny, loose dough forms, 3 to 4 minutes, stopping to scrape sides and bottom of bowl.

Spray a medium bowl with cooking spray. Pour dough into bowl. Dust top of dough with remaining 2 teaspoons (6 grams) flour, and cover tightly with plastic wrap. Let rise in a warm, draft-free place (75°F/24°C) until doubled in size, about 30 minutes.

Spray a 13x9-inch baking pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan. Transfer dough to prepared pan. Using heavily floured hands, press dough evenly into bottom of pan. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, about 30 minutes.

Preheat oven to 350°F (180°C).

Sprinkle dough evenly with Browned Butter Streusel.

Bake until edges start to brown, 25 to 30 minutes. Let cool completely in pan on a wire rack.

Using excess parchment as handles, remove cooled cake from pan. Using a serrated knife, cut cake in half horizontally. Spread Browned Butter Ermine Frosting onto bottom half of cake; spread preserves on top of frosting. Top with top half of cake, and refrigerate for at least 30 minutes. Garnish with confectioners’ sugar, if desired.