Preheat oven to 325°F (170°C). Spray a 9-inch square baking pan with baking spray with flour. Line bottom of pan with parchment paper.

In a medium bowl, whisk together flour, baking powder, Masala Chai Spice Mix, and salt.

In another medium bowl, whisk together brown sugar, milk, oil, granulated sugar, eggs, orange zest, and vanilla. Add sugar mixture to flour mixture, whisking just until combined. Pour into prepared pan.

Bake until edges are golden and a wooden pick inserted in center comes out clean, 30 to 35 minutes. Let cool in pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.

Trim ½ inch off each side of cake; set aside. Cut cake in half. Place half of cake on a cake plate. Spread 1 cup (180 grams) Orange-Dulce de Leche Buttercream on top. Place remaining half of cake on top. Spread remaining buttercream on top and sides of cake, swooping and texturing as desired.

Crumble cake trimmings. Decorate bottom edges of cake with cake crumbs. Refrigerate for at least 30 minutes before serving. Refrigerate in an airtight container for up to 5 days. If cake has been refrigerated for longer than 30 minutes, let stand at room temperature to soften buttercream before serving.