Prepare the Dough: In a stand mixer bowl, combine flour, salt, sugar, and yeast. Whisk together.
Mix Dough: Using the hook attachment on medium speed, gradually add room temperature water and mix until smooth, about 7-8 minutes.
First Proofing: Transfer dough to a floured surface, form into a ball, then place in a greased bowl. Cover and let proof in a warm spot until doubled in size, about an hour.
Second Proofing: Fold dough on itself, place in an oiled oven dish, stretch to fit, cover, and let prove again for an hour.
Confit Garlic: Place garlic in an oven dish with thyme, salt, and olive oil. Bake at 140°C (284°F) for 40 minutes. Cool at room temperature.
Prepare Onions: Place thick-sliced onions on a tray, drizzle with oil, season with salt, and bake at 200°C (392°F) for 10-12 minutes.
Assemble Focaccia: Drizzle garlic oil on dough, create holes with fingertips, insert confit garlic, top with onions and blue cheese.
Bake Focaccia: Bake at 200°C (392°F) for 25 minutes or until golden brown.