Add whole milk, honey, vanilla, and fresh, cold butter to your coffee mug.
Heat in the microwave until the butter melts, but be careful to avoid boiling.
Using a hand mixer (with one whisk) or immersion blender, whip these ingredients until they become frothy and the butter is visibly incorporated.
Poor hot, fresh coffee into your mug, to the strength you prefer.
Super simple, incredibly tasty.
For the stove top
Use a small saucepan, add your ingredients (except coffee), heat them up, blend them well, and poor them into your mug. Add hot, fresh coffee, and enjoy.
Notes
Avoid boiling to avoid curdling. No one wants curdled latte. Try a deeper saucepan for the stove top/hand mixer method to avoid splattering your arms with hot liquid.