For the syrup: Combine the golden syrup, cinnamon sticks, orange zest and juice in a small saucepan. Bring to a simmer over low heat. Remove from the heat and let steep for 30 minutes.
Remove and discard the cinnamon sticks. Return the syrup to low heat, bring just to a simmer and whisk in the butter. Keep warm.
For the French toast: Set a rack over a baking sheet and place inside the oven. Preheat the oven to 200 degrees F.
Whisk together the eggs, egg yolks, half and half, vanilla and cinnamon in a bowl until smooth. Arrange the biscuits, cut-side up, in a single layer in a large baking dish and pour the custard over. Let the biscuits soak, turning several times, for at least 30 minutes at room temperature or up to 4 hours refrigerated. (These biscuits must be soaked through.)
Heat half of the butter and oil in a large nonstick skillet over medium heat until the butter is melted and shimmering. Add 4 biscuit halves, cut-side down, and cook until deep golden brown, 4 to 5 minutes. Turn over and continue cooking until golden brown on the second side, another 3 to 4 minutes. (Don't rush the browning by turning up the heat the biscuits are dense and you want to cook them long enough to cook through.) Transfer the finished toasts to the baking rack. Repeat the process with the remaining butter, oil and biscuit halves.
Serve the French toast with the syrup and a dusting of confectioners' sugar.
Buttermilk Biscuits for French Toast:
Yield:8 to 10 biscuits
Preheat the oven to 450 degrees F. Line a baking sheet with parchment paper.
Combine the flour, baking powder, baking soda and salt in a large bowl. Cut in the butter using your fingers or a pastry cutter until the mixture resembles coarse meal. Add the buttermilk and gently mix until a dough just begins to come together.
Scrape the dough onto a lightly floured counter and pat into a 10-by-12-by-1-inch rectangle. Use a 3-inch round cutter to cut out biscuits. Reroll the scraps and cut again.
Put the biscuits on the prepared baking sheet, leaving a few inches between them, and brush the tops with cream. Bake until lightly golden brown, 12 to 15 minutes. Serve hot.