Slice the challah loaf into 1-inch-thick slices and arrange them in a single layer in a large baking dish.
In a bowl or the baking dish, whisk together the eggs, cream, vanilla extract, sugar, ground cinnamon, and 1/2 tablespoon of the instant coffee powder until well combined.
Press each slice of bread into the egg mixture and let soak about 30 seconds per side so it absorbs but does not fall apart.
Heat a skillet over medium heat and add 1 tablespoon of butter. When it foams, add soaked bread slices in a single layer and cook until the bottoms are golden brown, about 2–3 minutes.
Flip the slices, add more butter as needed (use your judgment), and cook the other side until golden and cooked through. Repeat with remaining slices and butter.
Stir the remaining 1/2 tablespoon instant coffee powder into the mascarpone with the honey until smooth.
Spread a thin layer of the mascarpone mixture on warm French toast slices, sprinkle lightly with cocoa powder, and serve with maple syrup and sliced strawberries.