Whisk active dry yeast (7g), honey (2 tsp), and warm water (2½ cups) in a medium bowl and let sit 10-15 minutes (it should foam or at least get creamy; if it doesn’t your yeast is dead and you should start again—check the expiration date!).
Add in all-purpose flour (625g) and salt (1 Tbsp) and mix with a rubber spatula until a shaggy dough forms and no dry streaks remain.
Pour olive oil (4 Tbsp) into a big bowl that will fit in your refrigerator. Transfer dough to bowl and turn to coat in oil. Cover with a silicone lid or plastic wrap and chill until dough is doubled in size (it should look very bubbly and alive), at least 8 hours and up to 1 day. If you're in a rush, you can also let it rise at room temperature until doubled in size, 3–4 hours.
Generously butter a 13x9" baking pan (for thicker focaccia that’s perfect for sandwiches), or an 18x13" rimmed baking sheet (for focaccia that's thinner and crispier). Pour olive oil (1 Tbsp) into center of pan.
Keeping the dough in the bowl and using a fork in each hand, gather up edges of dough farthest from you and lift up and over into center of bowl. Give the bowl a quarter turn and repeat process. Do this 2 more times; you want to deflate dough while you form it into a rough ball. Transfer dough to prepared pan. Pour any oil left in bowl over and turn dough to coat it in oil. Let rise, uncovered, in a dry, warm spot (like on top of the fridge or a preheating oven) until doubled in size, at least 1½ hours and up to 4 hours.
Place a rack in middle of oven; preheat to 230°C. To see if the dough is ready, poke it with your finger. It should spring back slowly, leaving a small visible indentation. If it springs back quickly, the dough isn’t ready. (If at this point the dough is ready to bake but you aren’t, you can chill it up to 1 hour.) Lightly oil your hands. Gently stretch out dough to fill pan/tray if needed. Dimple focaccia all over with your fingers, like you’re aggressively playing the piano, creating very deep depressions in the dough (reach your fingers all the way to the bottom of the pan).
Drizzle with remaining olive oil (1 Tbsp) and sprinkle with flaky sea salt. Bake focaccia until puffed and golden brown all over, 20–30 minutes.
Notes
Focaccia is best eaten the day it's made, but keeps well in the freezer. Slice it into pieces, store it in a freezer-safe container, then reheat it on a baking sheet in a 150°C oven.