Preheat the oven to 180C. Line a baking sheet with some parchment. In a bowl, mix the strawberries with sugar and lemon juice, then scatter them on the baking sheet. Bake for 30 minutes.
In a large pie dish, whisk egg, buttermilk, vanilla until combined. Place the bread slices in the batter and let them soak for a few minutes on each side. When completey soaked and soft, squeeze the excess of liquid out of them and place them on a separate plate until ready to use. Heat a large skillet over medium-high heat and melt the butter. When hot, add the bread slices and fry until deeply golden on both sides, about 5 minutes per side.