Place eggs, eggnog, vanilla extract, nutmeg, cinnamon and salt into a large bowl and whisk until well combined.: You will notice the mixture becoming smooth and slightly frothy, with the eggnog aroma blending with spice notes, which signals even distribution; whisking creates a uniform custard so every bite has the same flavor and texture, and a common mistake here is under-mixing so spices remain clumpy, so take a little extra time to whisk until the color is even.
Place approximately 1-2 teaspoons of butter into a medium size skillet and heat over medium heat. Once skillet is hot, dip one piece of brioche bread into the egg and milk mixture, let extra liquid drip back into the bowl, then transfer to prepared pan.: The butter should melt and foam without browning immediately, producing a nutty scent that tells you the pan is ready; medium heat gives steady browning without burning, and a typical error is overheating which will burn the butter and impart bitterness, so keep the temperature moderate and watch for gentle sizzling.
Bake until golden on each side, approximately 2-3 minutes each. Repeat with remaining slices of bread, adding more butter to the pan as needed. Serve hot with butter, syrup and berries.: You will feel the bread soak but still hold shape when lifted, and the custard should coat the slice evenly; letting excess drip prevents a soggy pan and helps create a golden crust, and people often leave bread to soak too long which results in collapse, so a quick dunk is usually best unless your bread is very stale and needs more time.
Bake until golden on each side, approximately 2 to 3 minutes each: As the slice cooks you will hear a gentle sizzle and see edges firming and turning a deep golden brown, which is the cue to flip; this color indicates Maillard reaction and a toasted flavor, and a frequent issue is flipping too early before the bottom sets, causing the slice to fall apart, so wait until a spatula lifts cleanly.
Repeat with remaining slices of bread, adding more butter to the pan as needed: The pan will develop fond from previous slices, contributing flavor, and replenishing butter ensures even browning for each batch; if you skip adding fat the next slices may stick or brown unevenly, so keep a little extra butter handy and wipe out burned bits between batches if necessary.
Serve hot with butter, syrup and berries: Hot slices will steam slightly when plated and the aroma will be most pronounced, enhancing the perception of richness; serving immediately preserves the contrast between crisp exterior and soft interior, and a common slip is letting the toast sit too long which leads to sogginess, so plate and enjoy at once for best texture.