Preheat oven to 300°F (150°C).: Warm air and a steady low temperature create even baking for this deep Bundt shape, which helps the center cook without the edges overbrowning. You should feel a gentle rise in the smell of warm kitchen air as the oven comes to temp. A common mistake is rushing to bake in an oven that is not fully heated, which can cause uneven rise and a dense center, so always wait until the oven indicator shows stable heat.
In a spice grinder, combine 1/4 cup (50 grams) sugar and lavender; process until lavender is finely ground and mixture is combined. Transfer to a small bowl, and add remaining 1 3/4 cups (350 grams) sugar, stirring until well combined.: The scent should open up as the lavender is ground, releasing sweet floral oils into the sugar so the aroma becomes warm and fragrant rather than sharp. The texture of the lavender sugar will be powdery and slightly perfumed, which helps disperse flavor evenly in the batter. Avoid leaving large pieces of lavender, since they can create bitter pockets; if you find clumps, regrind briefly.
In a large bowl, whisk together 1 1/2 cups (300 grams) lavender sugar, oil, eggs, 1/2 cup (170 grams) honey, lemon zest, and vanilla until well combined.: You will notice the mixture thicken and glisten as the oil and honey emulsify with the eggs, and the lemon zest releases bright citrus oils that pop visually and aromatically. The batter will smell floral, sweet, and citrusy, which is the goal. A common issue here is over-whisking, which can incorporate too much air and cause the cake to dome or crack, so whisk just until homogeneous.
In a medium bowl, whisk together flour, salt, and baking soda. Gradually add flour mixture to sugar mixture alternately with sour cream, beginning and ending with flour mixture, whisking just until combined after each addition and stopping to scrape sides of bowl.: As you fold in the cake flour and sour cream , the batter should become thick but still pourable, with no streaks of flour. The sour cream will smooth the batter and add a slight tang that balances sweetness. If you overmix, gluten will develop and the cake may be tough, so stop when the last streaks disappear and scrape the bowl cleanly.
Spray a 10-cup Bundt pan with baking spray with flour. Pour batter into prepared pan. Tap pan on a kitchen towel-lined counter a few times to release any air bubbles. (Pan will be quite full, but batter will not overflow.): Filling the Bundt pan almost to the top is normal; the batter will settle as it bakes. Tapping helps bubbles surface and pop, preventing large tunnels in the crumb. Be mindful of spills, because sugary batter that drips can darken and smoke in the oven. If your pan seems overfull, use a small spatula to even the top rather than pressing down, which can degas the batter too much.
Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers at least 205°F (96°C), 1 hour and 12 minutes to 1 hour and 20 minutes, rotating pan after 50 minutes of baking and loosely covering with foil to prevent excess browning, if necessary. Let cool in pan for 20 minutes. Using a small offset spatula, gently loosen cake from center and edges of pan. Invert cake onto a wire rack; gently tap wire rack with pan on counter a few times to help loosen cake. Remove pan, and place wire rack on a rimmed baking sheet.: As the cake bakes, the kitchen will fill with a warm, honeyed floral aroma and the crust should develop a deep golden color. Rotating the pan encourages even color, and tenting with foil stops the top from getting too dark. Cooling in the pan for the prescribed time lets the crumb set so the cake releases cleanly; forcing it too soon risks breakage. If the cake sticks, wait a few extra minutes and try again, sliding a small offset spatula around the edges carefully.
In a small microwave-safe bowl, heat remaining 2 tablespoons (42 grams) honey on high in 10-second intervals, stirring between each, until loose and fluid. Quickly and carefully brush over warm cake. Let cake cool completely.: Warm honey is thinner and spreads easily, producing a shiny, slightly sticky surface that locks in moisture and enhances color. The aroma will intensify as the honey heats and melds with the lavender scent. Be cautious with hot honey, and brush gently to avoid gouging the soft crumb. A frequent mistake is waiting too long to brush, which makes the honey less likely to adhere and reduces the glossy finish.
Cover cooled cake with remaining 1/2 cup (100 grams) lavender sugar, gently pressing to adhere.: The final sugar coating should feel slightly velvety and fragrant, giving each slice a faint sparkle and a whisper of lavender on the tongue. Press lightly so the sugar bonds to the honey layer without dissolving completely, preserving texture contrast. If you press too hard, you may embed sugar into the crust and lose the delicate visual effect, so a gentle touch is best.