Preheat the oven to 350°F (175°C). Grease a 9×13-inch pan (or line with parchment for easy lifting).

In a large bowl, combine the flour, sugars, spices, leavening, and salt.

In another bowl, whisk together the eggs, melted butter, oil, buttermilk, and vanilla until smooth.

Add the wet ingredients to the dry ingredients, and mix just until combined.

Fold in the finely shredded carrots and nuts (and any variations).

Spread into the pan and bake 30–36 minutes, or until the center springs back and a tester comes out clean.

Cool completely before frosting.

Melt the butter in a saucepan over medium heat. Cook, stirring often, until the butter foams, the milk solids turn deep golden, and it smells toasty (usually 5–7 minutes).

Transfer to a heatproof bowl and chill it until it’s opaque and just starting to firm up (about 30–40 minutes in the refrigerator).

{You don’t want it fully solid; you just want it soft but scoopable.}

In a mixing bowl, beat the cream cheese until smooth. Add the cooled browned butter and mix until fully incorporated.

Add 3 cups (330g) of confectioners’ sugar, vanilla, and salt. Beat until light and creamy. If you want it thicker, add the remaining sugar ¼ cup at a time.